Principal Component Analysis of the Hamilton Anxiety Scale by Hamilton (1969) [N = 115] and Pichot et al (1981) [N = 411]
\r\n\tNeuromorphic engineering groups are joining together specialized researchers in the most diverse fields since they are mathematicians, physicists, biologists, psychologists and engineers of the most diverse branches.
\r\n\tThe main objective of this book is to provide an overview of the field of neuromorphic engineering, as well as the most outstanding advances in recent years.
Most of the scales we use in clinical psychiatry when measuring mood and anxiety were developed more that three decades ago. Thus the Hamilton Anxiety Scale (HAM-A) (Hamilton 1969) is still the internationally most used clinician-rated scale within states of clinical anxiety, whereas Spielberger’s State Anxiety Scale (Spielberger, Gorsuch & Lushene 1970) or the Symptom Checklist (SCL-90) (Derogatis et al. 1974) are among the most frequently used patient-rated questionnaires.
\n\t\t\tIn her comprehensive content analysis of the items included in 27 different rating scales or questionnaires for clinical anxiety, de Bonis (1974) concluded that the HAM-A seems to cover the clinically most representative items for states of generalized anxiety. This can be considered in itself as one way of demonstrating the clinical validity of the HAM-A.
\n\t\t\tAs concerns questionnaires, the Spielberger State Anxiety Scale covers the psychic anxiety symptoms whereas the anxiety subscale of the SCL-90 contains more somatic anxiety symptoms than psychic anxiety symptoms (Derogatis et al. 1974).
\n\t\t\tAlthough the SCL-90 includes some specific anxiety subscales, e.g., a phobia and an obsessive-compulsive (OCD) subscale, these anxiety subscales are also not sufficiently valid. The measurement of panic attacks is probably most validly measured in terms of minor versus major attacks, i.e. global assessments. The measurement of states of OCD is probably most validly measured by the duration of this state of anxiety, e.g. less or more than two hours daily. The Anxiety-Symptom-Scale (ASS) is shown in the Appendix as an example of a very short screening questionnaire covering the many subtypes of states of anxiety. In the following, it is the general state of anxiety as measured archetypically by the HAM-A, and by the corresponding self-rating scales that will be treated.
\n\t\t\tThe psychometric validation of these general anxiety scales became important with reference to the classes of drugs most frequently investigated in trials of anti-anxiety medication, namely tricyclic antidepressants (e.g., imipramine) versus benzodiazepines (e.g., diazepam). Early on, Derogatis et al (1974) demonstrated that whereas imipramine was superior to diazepam when using the SCL-90 subscale of depression, no differences were obtained when using the SCL-90 anxiety subscale. The landmark study in this respect was the study by Rickels et al (1993) which demonstrated that when treating patients with generalized anxiety disorder with imipramine versus diazepam in a placebo-controlled, randomised trial, imipramine was superior to benzodiazepine on the psychic factor in the HAM-A but not on the somatic factor in the HAM-A.
\n\t\t\tThese results led to a change in the algorithm of generalized anxiety from DSM-III to DSM-IV so that the number of somatic anxiety symptoms was reduced. However in the ICD-10 diagnostic manual (World Health Organization 1993) the number of somatic anxiety symptoms outranged the number of psychic anxiety symptoms in the algorithm of generalized anxiety disorder.
\n\t\t\tThe following will treat the specific psychometrically valid methods (principal components analysis, factor analysis and item response theory analysis) in order to indicate how to use HAM-A and SCL-90 in trials of anti-anxiety drugs.
\n\t\tIn clinical psychometrics we often describe principal components analysis (PCA) or factor analysis (FA) as the classical methods of validation while item response theory analysis (IRT) is seen as the modern method (\n\t\t\t\t\tBech et al. 2011\n\t\t\t\t).
\n\t\t\tHistorically, PCA was published at a later date than Spearman’s two factor models of intelligence (Spearman 1904, Spearman 1927), namely by Hotelling (1933). When modifying a factor analysis with our sophisticated electronic programs, e.g. SPSS or SAS, we start today with PCA and then, if necessary, go for various forms of rotations in the so-called exploratory FA (Child 2006).
\n\t\t\tIRT analysis is used to evaluate to what extent the total score of a scale is sufficient when measuring the clinical effect of anti-anxiety drugs. We have both a parametric IRT model (Rasch 1960) and a non-parametric model (Mokken 1971). In the following, only Mokken analysis will be referred to.
\n\t\tThe first version of the HAM-A (Hamilton 1959) consisted of 13 items, whereas the revised version (Hamilton 1969) included 14 items (see Appendix). Hamilton released his HAM-A14 with reference to principal components analysis (PCA) on 115 patients (including patients with both primary anxiety states (N = 42) and patients with anxiety secondary to somatic disorders (N = 53)). Table 1 shows the results. The first principal component is clearly a general factor in which all the 14 items have positive loadings. The second principal component is a bi-directional, or dual factor with positive loadings on the psychic symptoms of anxiety and negative loadings on the somatic anxiety symptoms. Table 1 also shows the results from the study by Pichot et al (1981) on 411 patients from the family doctor setting with a mixture of primary and secondary states of anxiety. Pichot et al (1981) employed both a PCA approach and an exploratory factor analysis (FA) with varimax rotation. Essentially, Pichot et al (1981) found no extra information in the FA with rotation. As shown in Table 1, the PCA results of Pichot et al (1981) are very similar to those obtained by Hamilton (1969). The first principal component is obviously a general factor while the second principal component is a bi-directional factor. In the original publication by Pichot et al (1981) the sign of the second principal component loadings is actually the opposite of the signs published by Hamilton (1969), but this type of loading (negative and positive) is just a technical or topographical issue (Child 2006). The second principal component identified by Pichot et al (1981) contrasts psychic versus somatic symptoms of anxiety corresponding to Hamilton (1969).
\n\t\t\t\t\n\t\t\t\t\t\t\t\tItems\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tGeneral factor\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tDual factor\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t||
\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\tHamilton (1969)\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tPichot et al (1981)\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tHamilton (1969)\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tPichot et al (1981)\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Anxious mood \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.66 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.50 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.50 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.39 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Tension \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.83 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.62 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.32 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.35 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Fears \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.49 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.45 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.29 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.35 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Insomnia \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.52 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.65 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.05 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.26 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Concentration \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.69 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.62 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.37 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.27 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Depressed mood \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.69 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.66 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.33 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.38 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Somatic (muscular) \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.52 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.54 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.53 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.25 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Somatic (sensory) \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.73 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.58 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.30 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t- 0.40 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Cardiovascular \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.68 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.53 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.41 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t- 0.48 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Respiratory \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.56 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.52 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.40 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.43 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Gastro-intestinal | \n\t\t\t\t\t\t\t0.66 | \n\t\t\t\t\t\t\t0.29 | \n\t\t\t\t\t\t\t-0.16 | \n\t\t\t\t\t\t\t-0.39 | \n\t\t\t\t\t\t
Genito-urinary \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.45 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t0.33 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.25 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t-0.31 \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Other autonomic | \n\t\t\t\t\t\t\t0.67 | \n\t\t\t\t\t\t\t0.52 | \n\t\t\t\t\t\t\t-0.14 | \n\t\t\t\t\t\t\t-0.30 | \n\t\t\t\t\t\t
Behaviour at interview | \n\t\t\t\t\t\t\t0.60 | \n\t\t\t\t\t\t\t0.70 | \n\t\t\t\t\t\t\t0.10 | \n\t\t\t\t\t\t\t- 0.09 | \n\t\t\t\t\t\t
Principal Component Analysis of the Hamilton Anxiety Scale by Hamilton (1969) [N = 115] and Pichot et al (1981) [N = 411]
The usefulness of this two factor model of the HAM-A14 was demonstrated by Rickels et al (1993) in a double-blind, placebo-controlled trial comparing diazepam with imipramine in patients with a DSM-III diagnosis of generalized anxiety disorder. Imipramine was found superior to diazepam on the psychic anxiety symptoms (Table 1) on HAM-A, while both imipramine and diazepam were superior to placebo on the somatic anxiety symptoms (Table 1). However, among the psychic anxiety symptoms in HAM-A (Table 1) are such items as depressed mood and sleep.
\n\t\t\t\tClinical validity was examined in a trial focussing on a 6-item HAM-A subscale (HAM-A6) comprising five psychic anxiety symptoms (anxious mood, psychic tension, fears, intellectual difficulties, and anxious behaviour) and one somatic anxiety symptom (muscular tension) (Bech 2007). This group of HAM-A symptoms covering the core symptoms of generalized anxiety disorder is in accordance with the study by Snaith et al (1982).
\n\t\t\t\tThe analyses performed by Meoni et al (2001) revealed that the HAM-A6 items were among the symptoms in patients with DSM-IV generalized anxiety disorder with the most significant discrimination between venlafaxine and placebo.
\n\t\t\t\tThe HAM-A6 was compared to the HAM-A14 in order to evaluate the two scales’ psychometric validity, using Mokken’s non-parametric IRT model (Bech 2007). In this study the four placebo-controlled trials with fixed doses of pregabalin in patients with generalized anxiety disorder were combined, and Mokken analysis identified a coefficient of homogeneity of 0.35 for HAM-A14 while HAM-A6 reached 0.46 (Bech 2007). A coefficient of homogeneity of 0.40 or higher is, in accordance with Mokken (1971), required to able to state that the total score of a scale is a sufficient statistic.
\n\t\t\t\tThe pregabalin dose-response relationship study was performed on six of the available placebo-controlled trials (Bech 2007). One US trial was excluded from the analysis because more than 30% of the patients dropped out during the planned trial period of 4 weeks. The quality of a trial is, among other things, evaluated by the percentage of patients completing the planned short-term study, and 70% is used in this context (Angst et al. 1989). Another trial (Montgomery et al. 2006) was excluded because the HAM-A14 baseline mean score was higher than the mean score of the other trials (27.4 versus 24.5 (P < 0.01)) and because the age of the patients was high (44.0 (12) versus 37.2 (10) (P < 0.01)) (Bech 2007).
\n\t\t\t\tEffect size was used as response criterion in this pooled analysis of the four trials with sufficient homogeneity. An effect size of 0.40 or higher was considered to be evidence of a clinically significant effect of pregabalin compared to placebo (Bech 2007). A dose of 150 mg pregabalin over four weeks proved to obtain an effect size between 0.17 and 0.22 on HAM-A6; and between 0.24 and 0.38 on HAM-A14, i.e. not clinically significant. In a dose range between 200 mg and 450 mg daily, the pregabalin effect size was between 0.44 and 0.55 on the HAM-A6 and 0.37 and 0.68 on the HAM-A14. A dose of 600 mg pregabalin daily did not increase the effect size, as the range on the HAM-A6 was between 0.36 and 0.50 (Bech 2007).
\n\t\t\t\tThe trial excluded from this pooled analysis due to a significantly higher baseline HAM-A14 and patient age is the study by Montgomery et al (Montgomery et al. 2006). Table 2 shows the results after 4 weeks of therapy in the Montgomery et al study (2006), using effect size as response criterion. The HAM-A6 effect size of both 400 and 600 mg pregabalin was between 0.28 and 0.30, while the effect size of 75 mg venlafaxine daily over four weeks reached a level of 0.40 (Bech 2007). In Table 2 the effect size for the HAM-A item of sleep is included, here the results show that the effect size was clearly above 0.40 for both doses of pregabalin whereas the venlafaxine effect size was below 0.40; indicating that venlafaxine is a non-sedating drug.
\n\t\t\t\t\n\t\t\t\t\t\t\t\tTreatment\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tEffect size\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t||
\n\t\t\t\t\t\t\t\tHAM-A6\n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tHAM-A14\n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tSleep\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t|
Pregabalin 400 mg daily (N = 97) | \n\t\t\t\t\t\t\t0.30 | \n\t\t\t\t\t\t\t0.38 | \n\t\t\t\t\t\t\t0.65 | \n\t\t\t\t\t\t
Pregabalin 600 mg daily (N = 110) | \n\t\t\t\t\t\t\t0.28 | \n\t\t\t\t\t\t\t0.31 | \n\t\t\t\t\t\t\t0.54 | \n\t\t\t\t\t\t
Venlafaxine 75 mg daily (N = 113) | \n\t\t\t\t\t\t\t0.40 | \n\t\t\t\t\t\t\t0.31 | \n\t\t\t\t\t\t\t0.33 | \n\t\t\t\t\t\t
The placebo-controlled trial by Montgomery et al (2006) with two fixed pregabalin doses and the active comparator venlafaxine. In the placebo arm N = 101. The results with effect size according to Bech (2007)
\n\t\t\t\t\tLydiard et al (2010) have made an analysis of all six placebo-controlled pregabalin trials in generalized anxiety disorder, showing the change from baseline to endpoint on the individual HAM-A items. This analysis confirmed that no difference was seen between 450 mg and 600 mg pregabalin daily compared to placebo for the HAM-A6 items. For the HAM-A14 item of depressed mood, however, 600 mg pregabalin was statistically more effective than 450 mg when compared to placebo (P < 0.01 versus P < 0.05), (Lydiard et al. 2010).
\n\t\t\t\tThere are still very few instances in which HAM-A6 and HAM-A14 have been used in trials with new generation antidepressants in patients with generalized anxiety disorder. An effect size of 0.38 was obtained on HAM-A14 in a placebo-controlled trial with sertraline (Allgulander et al. 2004). For venlafaxine Mitte et al (2005) obtained an effect size of 0.30 on HAM-A14 when pooling five placebo-controlled trials in patients with generalized anxiety disorder.
\n\t\t\t\tFor duloxetine we only have one fixed dose trial in a placebo-controlled design in the treatment of generalized anxiety disorder over a 9 week period (Koponen et al. 2007). Based on the published results it was not possible to calculate effect size correctly (Koponen et al. 2007). However, the estimation of sample size in the Koponen et al study (2007) was based on the assumption that the pooled standard deviation of the change score on HAM-A14 from baseline to endpoint was 6.0, and that the difference in mean change score was 2.0 for duloxetine minus placebo. In this case, the effect size of 2/6, or 0.33, was accepted, i.e. at the level of venlafaxine (Table 2) for the HAM-A.
\n\t\t\tThe most comprehensive anxiety self-rating scale is the Symptom Checklist (SCL-90). Hamilton never developed a self-rating scale corresponding to his HAM-A14. The original form of the SCL was developed by Parloff et al (1954). Historically, the final version was developed by Derogatis et al (1974), while the different subscales were most precisely defined by Bech (1993). In a review Cyr et al (1985) discussed the factor structure of the SCL-90, concluding that principal component analysis (PCA) seems to identify the first principal component as a general factor, because all the 90 items are more or less positively correlated. However, exploratory factor analysis with varimax rotation as performed by Lipman et al (1977), obtaining a nine-factor solution, has been used in several studies with the SCL-90. The anxiety subscale from this solution has never been accepted as a sufficient scale in trials of anti-anxiety drugs.
\n\t\t\t\tWhen using an unselected sample of patients treated in our Day Hospital at the Psychiatric Centre of North Zealand in Denmark (N = 555) we demonstrated with the SCL-90 that PCA identified as the first principal component a general factor reflecting that all the 90 items are more or less positively correlated (Bech et al. 2010). The second principal component was a bi-directional factor with depression items at one pole and anxiety items at the opposite.
\n\t\t\t\tWe had previously identified a SCL depression subscale (SCL-D6) with six items corresponding to the HAM-D6. Now we selected from the second principal component the anxiety items with the highest loadings. When these items had been subjected to another PCA, we could demonstrate the contrast between psychic anxiety items and somatic anxiety items. This SCL-A20 anxiety subscale is very similar to the HAM-A14. The SCL-D6 and the SCL- A20 are shown in the Appendix.
\n\t\t\t\t\n\t\t\t\t\tTable 3 shows the results from a data set obtained by Danish psychiatrists in private practice (chaired by Drs. Bodil Andersen, Bettina N. Holm and Niels-Anton Rasmussen) who now use the SCL-90 in their daily routine. In Table 3 the four most frequent ICD-10 depression diagnoses are shown at the top. The mean score on the depression scale (SCL-D6) for dysthymia is approximately 10; this is the cut-off score for clinical depression. The mean scores on SCL-D6 do increase from the category of mild depression to that of severe depression (Table 3). With regard to the anxiety subscale (SCL-A20), the cut-off score for clinical anxiety is 30. The category of dysthymia obtained a mean score on the SCL-A20 just below 30 whereas the mean score for the depression categories increased with increasing degree of depression.
\n\t\t\t\t\n\t\t\t\t\t\t\t\tDiagnosis Code\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tCategory\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tNumber of observations\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tSCL-D6\n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\tSCL-A20\n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t |
F 34.1 | \n\t\t\t\t\t\t\tDysthymia | \n\t\t\t\t\t\t\t(N = 43) | \n\t\t\t\t\t\t\t10.38 | \n\t\t\t\t\t\t\t29.40 | \n\t\t\t\t\t\t
F 32.0 | \n\t\t\t\t\t\t\tDepression, mild | \n\t\t\t\t\t\t\t(N = 192) | \n\t\t\t\t\t\t\t11.70 | \n\t\t\t\t\t\t\t33.00 | \n\t\t\t\t\t\t
F 32.1 | \n\t\t\t\t\t\t\tDepression, moderate | \n\t\t\t\t\t\t\t(N = 171) | \n\t\t\t\t\t\t\t12.12 | \n\t\t\t\t\t\t\t34.00 | \n\t\t\t\t\t\t
F 32.2 | \n\t\t\t\t\t\t\tDepression, severe | \n\t\t\t\t\t\t\t(N = 52) | \n\t\t\t\t\t\t\t13.20 | \n\t\t\t\t\t\t\t37.00 | \n\t\t\t\t\t\t
F 34.1 | \n\t\t\t\t\t\t\tDysthymia | \n\t\t\t\t\t\t\t(N = 43) | \n\t\t\t\t\t\t\t10.38 | \n\t\t\t\t\t\t\t29.40 | \n\t\t\t\t\t\t
F 43.0 | \n\t\t\t\t\t\t\tAcute stress reaction | \n\t\t\t\t\t\t\t(N = 58) | \n\t\t\t\t\t\t\t9.36 | \n\t\t\t\t\t\t\t27.00 | \n\t\t\t\t\t\t
F 41.2 | \n\t\t\t\t\t\t\tMixed anxiety/depression | \n\t\t\t\t\t\t\t(N = 28) | \n\t\t\t\t\t\t\t9.90 | \n\t\t\t\t\t\t\t29.00 | \n\t\t\t\t\t\t
F 41.1 | \n\t\t\t\t\t\t\tGeneralized anxiety disorder | \n\t\t\t\t\t\t\t(N = 68) | \n\t\t\t\t\t\t\t11.28 | \n\t\t\t\t\t\t\t36.40 | \n\t\t\t\t\t\t
F 43.1 | \n\t\t\t\t\t\t\tPosttraumatic stress disorder | \n\t\t\t\t\t\t\t(N = 40) | \n\t\t\t\t\t\t\t13.50 | \n\t\t\t\t\t\t\t43.20 | \n\t\t\t\t\t\t
Standardization: SCL-D6: A total score of 10 or more equals clinical depression SCL-A20: A total score of 10 or more equals clinical anxiety
\n\t\t\t\t\tTable 3 also shows the four most frequent ICD-10 categories for anxiety, namely acute stress reaction, mixed anxiety-depression, generalized anxiety disorder, and PTSD (post-traumatic stress disorder). On the SCL-D6, the cut-off score of 10 is obtained for GAD and PTSD, but not for mixed anxiety-depression which is in accordance with the ICD-10 criteria for this category. On the SCL-A20 the cut-off score for clinical depression is obtained for GAD and PTSD but not for mixed anxiety-depression, which is in concordance with the ICD-10 criteria for this category.
\n\t\t\tCompared to the Hamilton Depression Scale (HAM-D) the Hamilton Anxiety Scale (HAM-A) has obtained a status as the international standard for anxiety measurement with a major impact on the item profiles of generalized anxiety disorder from DSM-IV to DSM-IV. We do not yet have the final version of DSM-V. As regards the ICD-10, research with HAM-A14 has shown that the category of generalized anxiety disorder according to ICD-10 is too biased in favour of the somatic anxiety symptoms. A revision of ICD-10, ICD-11, will be released around 2015. In the mean time the HAM-A14 is the most appropriate measure for generalized anxiety research. The HAM-A14 version shown in the Appendix was developed with the acceptance of Max Hamilton himself (Bech, Kastrup & Rafaelsen 1986). The correct use of the HAM-A is to focus on the HAM-A6 in which the total score should be considered as a sufficient statistic.
\n\t\t\tMax Hamilton never constructed a self-rating version of his HAM-A14. The SCL-A20 included in the Appendix can be considered as a form of self-reported state of anxiety corresponding to HAM-A14. As indicated in the Appendix, nine of the symptoms measure psychic anxiety and 11 items measure the somatic anxiety syndrome.
\n\t\tAll the scales shown below are in the public domain.
\n\t\t\tAnxiety Symptom Scale (ASS)
The Hamilton Anxiety Scale (HAM-A14)
Scoring Sheet
Manual
SCL-D6\n\t\t\t\t\t
SCL-A20\n\t\t\t\t\t
The following questions ask about how you have been feeling over the past two weeks. Please put a tick in the box that is closest to how you have been feeling.
\n\t\t\t\t\n\t\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
Symptom scale
When interpreting the ASS, first determine whether Item 10 (symptom impact on daily functioning) has a score of 3 or more. If this is the case, then determine which of the nine anxiety symptoms has the highest score, and thereafter whether there is a score on the top three symptoms; these are the true anxiety symptoms.
\n\t\t\t\tWhen measuring treatment effect it is of course possible to use the total score.
\n\t\t\tNo. | \n\t\t\t\t\t\t\t\tSymptom | \n\t\t\t\t\t\t\t\tScore | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
1 | \n\t\t\t\t\t\t\t\tAnxious mood | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
2 | \n\t\t\t\t\t\t\t\tTension | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
3 | \n\t\t\t\t\t\t\t\tFears | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
4 | \n\t\t\t\t\t\t\t\tInsomnia | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
5 | \n\t\t\t\t\t\t\t\tDifficulties in concentration and memory | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
6 | \n\t\t\t\t\t\t\t\tDepressed mood | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
7 | \n\t\t\t\t\t\t\t\tGeneral somatic symptoms (Muscular symptoms) | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
8 | \n\t\t\t\t\t\t\t\tGeneral somatic symptoms (Sensory) | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
9 | \n\t\t\t\t\t\t\t\tCardiovascular symptoms | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
10 | \n\t\t\t\t\t\t\t\tRespiratory symptoms | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
11 | \n\t\t\t\t\t\t\t\tGastrointestinal symptoms | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
12 | \n\t\t\t\t\t\t\t\tGenito-urinary symptoms | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
13 | \n\t\t\t\t\t\t\t\tOther autonomic symptoms | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
14 | \n\t\t\t\t\t\t\t\tBehaviour during interview | \n\t\t\t\t\t\t\t\t0-4 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
\n\t\t\t\t\t\t\t\t | Total score | \n\t\t\t\t\t\t\t\t0-56 | \n\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | ||
Symptoms scored from 0 to 4 \n\t\t\t\t\t\t\t\t\t 0 = not present 1 = mild degree 2 = moderate degree 3 = marked degree 4 = maximum degree | \n\t\t\t\t\t\t\t\tSum 6 to 14 = mild anxiety 15 to 28 = moderate anxiety 29 to 52 = severe anxiety \n\t\t\t\t\t\t\t\t | \n\t\t\t\t\t\t\t
Hamilton scale
\n\t\t\t\t\t\tAnxiety \n\t\t\t\t\t
\n\t\t\t\t\tThis item covers the emotional condition of uncertainty about the future, ranging from worry, insecurity, irritability, apprehension to overpowering dread. The patient’s report of worrying, insecurity, uncertainty, fear and panic, i.e, the psychic, or mental (“central”) anxiety experience is to be found significant.
\n\t\t\t\t\t0: The patient is neither more nor less insecure or irritable than usual.
\n\t\t\t\t\t1: The patient reports more tension, irritability or feeling more insecure than usual.
\n\t\t\t\t\t2: The patient expresses more clearly to be in a state of anxiety, apprehension or irritability, which he may find difficult to control. It is thus without influence on the patient\'s daily life, because the worrying still is about minor matters
\n\t\t\t\t\t3: The anxiety or insecurity is at times more difficult to control because the worrying is about major injuries or harms which might occur in the future. E.g.: The anxiety may be experienced as panic, i.e. overpowering dread. Has occasionally interfered with the patient\'s daily life.
\n\t\t\t\t\t4: The feeling of dread is present so often that it markedly interferes with the patient\'s daily life.
\n\t\t\t\t\t\n\t\t\t\t\t\tTension \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes inability to relax, nervousness, bodily tensions, trembling and restless fatigue.
\n\t\t\t\t\t0: The patient is neither more nor less tense than usual.
\n\t\t\t\t\t1: The patient indicates to be somewhat more nervous and tense than usual.
\n\t\t\t\t\t2: The patient expresses clearly to be unable to relax, full of inner unrest which he finds difficult to control, but still without influence on the patient\'s daily life.
\n\t\t\t\t\t3: The inner unrest and nervousness is so intense or so frequent that it occasionally has interfered with the patient\'s daily work.
\n\t\t\t\t\t4: Tensions and unrest interfere with the patient\'s life and work at all times.
\n\t\t\t\t\t\n\t\t\t\t\t\tFears \n\t\t\t\t\t
\n\t\t\t\t\tA type of anxiety that arises when the patient finds himself in special situations. Such situations may be open or closed rooms, to queue, to ride a bus or a train. The patient shall experience relief by avoiding such situations. It is important to notice at this evaluation, whether there has been more phobic anxiety during the present episode than usual.
\n\t\t\t\t\t0: Not present.
\n\t\t\t\t\t1: Doubtful if present.
\n\t\t\t\t\t2: The patient has experienced phobic anxiety, but was able to fight it.
\n\t\t\t\t\t3: It has been difficult for the patient to fight or overcome his phobic anxiety which has thus to a certain extent interfered with the patient\'s daily life and work.
\n\t\t\t\t\t4: The phobic anxiety has clearly interfered with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tInsomnia \n\t\t\t\t\t
\n\t\t\t\t\tThis item covers only the patient\'s subjective experience of sleep length (hours of sleep per 24-hour-period) and sleep depth (superficial and interrupted sleep versus deep and steady sleep). The rating is based on the three preceding nights. Note: Administration of hypnotics or sedatives shall be disregarded.
\n\t\t\t\t\t0: Usual sleep length and sleep depth.
\n\t\t\t\t\t1: Sleep length is doubtfully or slightly reduced (e.g.due to difficulties failing asleep), but no change in sleep depth.
\n\t\t\t\t\t2: Sleep depth is now also reduced, sleep being more superficial. Sleep as a whole somewhat disturbed.
\n\t\t\t\t\t3: Sleep duration as well as sleep depth is markedly changed. The broken sleep periods total only a few hours per 24-hour-period.
\n\t\t\t\t\t4: It is here difficult to ascertain sleep duration as sleep depth is so shallow that the patient speaks of short periods of slumber or dosing, but no real sleep.
\n\t\t\t\t\t\n\t\t\t\t\t\tDifficulties in concentration and memory \n\t\t\t\t\t
\n\t\t\t\t\tThis item covers difficulties in concentration, making decisions about everyday matters, and memory.
\n\t\t\t\t\t0: The patient has neither more nor less difficulties in concentration and/or memory than usual.
\n\t\t\t\t\t1: It is doubtful whether the patient has difficulties in concentration and/or memory.
\n\t\t\t\t\t2: Even with a major effort it is difficult for the patient to concentrate on his daily routine work.
\n\t\t\t\t\t3: More pronounced difficulties with concentration, memory, or descision making. E.g. has difficulties to read an article in a newspaper or watch a television programme right through. Scores 3 as long as the loss of concentration or poor memory has not clearly influenced the interview.
\n\t\t\t\t\t4: When the patient during the interview has shown difficulty in concentration and/or memory, and/or when decisions are reached with considerable delay.
\n\t\t\t\t\t\n\t\t\t\t\t\tDepressed mood \n\t\t\t\t\t
\n\t\t\t\t\tThis item covers both the verbal and the non-verbal communication of sadness, depression, despondency, helplessness and hopelessness.
\n\t\t\t\t\t0: Natural mood.
\n\t\t\t\t\t1: When it is doubtful whether the patient is more despondent or sad than usual. E.g. the patient indicates vaguely to be more depressed than usual.
\n\t\t\t\t\t2: When the patient more clearly is concerned with unpleasant experiences, although he still is without helplessness or hopelessness.
\n\t\t\t\t\t3: The patient shows clear non-verbal signs of depression and/or hopelessness.
\n\t\t\t\t\t4: The patient\'s remarks on despondency and helplessness or the non-verbal ones dominate the interview in which the patient cannot be distracted.
\n\t\t\t\t\t\n\t\t\t\t\t\tGeneral somatic symptoms (muscular symptoms) \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes weakness, stiffness, soreness merging into real pain, which is more or less diffusely localised in the muscles. E.g. jaw ache or neck ache.
\n\t\t\t\t\t0: The patient is neither more nor less sore or stiff in his muscles than usual.
\n\t\t\t\t\t1: The patient indicates to be somewhat more sore or stiff in his muscles than usual.
\n\t\t\t\t\t2: The symptoms have gained the character of pain.
\n\t\t\t\t\t3: The muscle pains interfere to some extent which the patient\'s daily life and work.
\n\t\t\t\t\t4: The muscle pains are present most of the time and interfere clearly with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tGeneral somatic symptoms (sensory symptoms) \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes increased fatigability and weakness merging into real functional disturbances of the senses. Including: Tinnitus, blurring of vision, hot and cold flushes and prickling sensations.
\n\t\t\t\t\t0: Not present
\n\t\t\t\t\t1: It is doubtful whether the patient\'s indications of pressing or prickling sensations (e.g.,in ears, eyes or skin) are more pronounced than usual.
\n\t\t\t\t\t2: The pressing sensations in the ear reach the character of buzzing in the ears, in the eye as visual disturbances, and in the skin as prickling or itching sensations (paraesthesias).
\n\t\t\t\t\t3: The generalized sensory symptoms interfere to some extent with the patient\'s daily life and work.
\n\t\t\t\t\t4: The generalized sensory symptoms are present most of the time and interfere clearly with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tCardiovascular symptoms \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes tachycardia, palpitations, oppression, chest pain, throbbing in the blood vessels, and feelings of fainting.
\n\t\t\t\t\t0: Not present.
\n\t\t\t\t\t1: Doubtful if present.
\n\t\t\t\t\t2: Cardiovascular symptoms are present, but the patient can still control the symptoms.
\n\t\t\t\t\t3: The patient has now and again difficulties in controlling the cardiovascular symptoms which thus to some extent interfere with the patient\'s daily life and work.
\n\t\t\t\t\t4: The cardiovascular symptoms are present most of the time and interfere clearly with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tRespiratory symptoms \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes feelings of constriction or contraction in throat or chest, dyspnoea merging into choking sensations and sighing respiration.
\n\t\t\t\t\t0: Not present.
\n\t\t\t\t\t1: Doubtful if present.
\n\t\t\t\t\t2: Respiratory symptoms are present, but the patient can still control the symptoms.
\n\t\t\t\t\t3: The patient has now and again difficulties in controlling the respiratory symptoms which thus to some extent interfere with the patient\'s daily life and work.
\n\t\t\t\t\t4: The respiratory symptoms are present most of the time and interfere clearly with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tGastro-intestinal symptoms \n\t\t\t\t\t
\n\t\t\t\t\tThe item includes difficulties in swallowing, "sinking" sensation of the stomach, dyspepsia (heartburn or burning sensations in the stomach, abdominal pains related to meals, fullness, nausea and vomiting), abdominal rumbling and diarrhoea.
\n\t\t\t\t\t0: Not present.
\n\t\t\t\t\t1: Doubtful if present (or doubtful if different from the patient\'s ordinary gastrointestinal sensations).
\n\t\t\t\t\t2: One or more of the above-mentioned gastro-intestinal symptoms are present, but the patient can still control the symptoms.
\n\t\t\t\t\t3: The patient has now and again difficulties in controlling the gastrointestinal symptoms which thus to some extent interfere with the patient\'s daily life and work. E.g. tendency of losing control over the bowels.
\n\t\t\t\t\t4: The gastrointestinal symptoms are present most of the time and interfere clearly with the patient\'s daily life and work. E.g. losing control over the bowels.
\n\t\t\t\t\t\n\t\t\t\t\t\tGenito-urinary symptoms \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes non-organic or psychic symptoms such as frequent or more pressing passing of urine, menstrual irregularities, anorgasmia, dyspareunia, premature ejaculation, loss of erection.
\n\t\t\t\t\t0: Not present.
\n\t\t\t\t\t1: Doubtful if present (or doubtful if different from the ordinary genito-urinary sensations).
\n\t\t\t\t\t2: One or more of the above-mentioned genito-urinary symptoms are present, but they do not interfere with the patient\'s daily life and work.
\n\t\t\t\t\t3: The patient has now and again one or more of the above mentioned genito-urinary symptoms to such a degree that they to some extent interfere with the patient\'s daily life and work. E.g. tendency to lose control over micturition.
\n\t\t\t\t\t4: The genito-urinary symptoms are present most of the time and interfere clearly with the patient\'s daily life and work. E.g. losing control over micturition.
\n\t\t\t\t\t\n\t\t\t\t\t\tAutonomic symptoms \n\t\t\t\t\t
\n\t\t\t\t\tThis item includes dryness of mouth, blushing or pallor, sweating and dizziness. 0: Not present.
\n\t\t\t\t\t1: Doubtful if present.
\n\t\t\t\t\t2: One or more of the above-mentioned autonomic symptoms are present, but they do not interfere with the patient\'s daily life and work.
\n\t\t\t\t\t3: The patient has now and again one or more of the above-mentioned autonomic symptoms to such a degree that they to some extent interfere with the patient\'s daily life and work.
\n\t\t\t\t\t4: The autonomic symptoms are present most of the time and interfere clearly with the patient\'s daily life and work.
\n\t\t\t\t\t\n\t\t\t\t\t\tBehaviour at interview \n\t\t\t\t\t
\n\t\t\t\t\tThis item is based on patient behaviour during the interview. Did the patient appear tense, nervous, agitated, restless, fidgeting, tremulous, pale, hyperventilating, or sweating?
\n\t\t\t\t\tOn the basis of such observations a global estimate is made:
\n\t\t\t\t\t0: The patient does not appear anxious.
\n\t\t\t\t\t1: It is doubtful whether the patient is anxious.
\n\t\t\t\t\t2: The patient is moderately anxious.
\n\t\t\t\t\t3: The patient is clearly anxious.
\n\t\t\t\t\t4: The patient is overwhelmed by anxiety. E.g. shaking and trembling all over.
\n\t\t\t\t\n\t\t\t\t\t\t\t\t | \n\t\t\t\t\t\t
SCL-D6\n\t\t\t\t\t\t
Standardization:
\n\t\t\t\t0 – 6 : no depression
\n\t\t\t\t7 – 11: mild depression
\n\t\t\t\t12 – 17: moderate depression
\n\t\t\t\t18 – 24: severe depression
\n\t\t\tDuring the past week including today, how much were you bothered by: | \n\t\t\t\t\t\t\tNot at all | \n\t\t\t\t\t\t\tA little bit | \n\t\t\t\t\t\t\tModerately | \n\t\t\t\t\t\t\tQuite a bit | \n\t\t\t\t\t\t\tExtremely | \n\t\t\t\t\t\t|
31 | \n\t\t\t\t\t\t\tWorrying too much about things? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
2 | \n\t\t\t\t\t\t\tNervousness or shakiness inside? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
33 | \n\t\t\t\t\t\t\tFeeling fearful? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
57 | \n\t\t\t\t\t\t\tFeeling tense or keyed up? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
23 | \n\t\t\t\t\t\t\tSuddenly scared for no reason? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
17 | \n\t\t\t\t\t\t\tTrembling? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
72 | \n\t\t\t\t\t\t\tSpells of terror or panic? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
47 | \n\t\t\t\t\t\t\tFeeling afraid to travel on buses, subways or trains? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
25 | \n\t\t\t\t\t\t\tFeeling afraid to go out of your house alone? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
82 | \n\t\t\t\t\t\t\tFeeling afraid you will faint in public? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
55 | \n\t\t\t\t\t\t\tTrouble concentrating? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
42 | \n\t\t\t\t\t\t\tSoreness of your muscles? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
52 | \n\t\t\t\t\t\t\tNumbness or tingling in parts of your body? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
49 | \n\t\t\t\t\t\t\tHot or cold spells? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
12 | \n\t\t\t\t\t\t\tPains in heart or chest | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
39 | \n\t\t\t\t\t\t\tHeart pounding or racing? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
48 | \n\t\t\t\t\t\t\tTrouble getting your breath? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
40 | \n\t\t\t\t\t\t\tNausea or upset stomach? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
4 | \n\t\t\t\t\t\t\tFaintness or dizziness? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
78 | \n\t\t\t\t\t\t\tFeeling so restless you can’t sit still? | \n\t\t\t\t\t\t\t0 | \n\t\t\t\t\t\t\t1 | \n\t\t\t\t\t\t\t2 | \n\t\t\t\t\t\t\t3 | \n\t\t\t\t\t\t\t4 | \n\t\t\t\t\t\t
Total score | \n\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t | \n\t\t\t\t\t\t |
Standardization: A score between 20 and 29 is the risk zone of anxiety and a score of 30 or more is a clear clinical anxiety state
The measurement of states of anxiety by use of symptom rating scales such as the HAM-A14 is psychometrically most valid in generalized anxiety. Within such states of anxiety the factors of psychic anxiety versus somatic anxiety are important. The HAM-A6 covers the core items of the DSM-IV syndromes of generalized anxiety with most emphasis on the psychic anxiety symptoms. The SCL-A20 is the SCL-90 subscale to most validly cover the HAM-A14 symptoms.
\n\t\t\tThe Anxiety Symptom Scale (ASS) is useful as a screening instrument to cover the whole field of anxiety states, including phobia, panic, or OCD.
\n\t\tPolymer optical fibers (POF) are used in various fields of applications. The core material consists of polymethylmethacrylate (PMMA), while the cover is made of fluorinated PMMA. The whole fiber has a diameter of 1 mm, which is depicted in Figure 1. POFs are used for optical data transmission based on the same principle as glass fiber. As a communication medium, they offer a couple of advantages related to other data communication systems such as copper cables, glass fibers and wireless systems and have great potential to replace them in different applications.
\nComparison of optical fiber types.
In comparison with glass optical fibers (GOF), POFs are easy to use in the field because of low bending losses and a large optical core of 980 μm. This makes the POF very insensitive to rough and dusty environments as well as losses on plugs in comparison with glass fibers [1]. However, one advantage of using glass fibers is their low attenuation, which is below 0.2 dB/km in the infrared range. The attenuation of polymeric fibers in the visible spectrum from 350 to 750 nm (see Figure 2) is much more higher with its minimum of 85 db/km at a wavelength of 570 nm. For this reason, the use of POF in communication systems is focused on short distance communication from 10 to 100 m. The larger core diameter of POFs leads to high-mode dispersion of more than 2.2 millions of optical modes. Additionally, the high attenuation at wavelengths higher than 700 nm limits the application of the POF to the visible spectrum of light (400–700 nm). Here, POFs can outperform the current standard of copper cable as a communication medium. On the one hand, they feature lower weight, low bending radius and space. On the other hand, POFs are not susceptible to electromagnetic interference [2, 3]. For these reasons, POFs are already used in various application domains, for example, in the automotive sector and for in-house communication [4, 5, 6, 7].
\nAttenuation of POF in the visible range [1].
Typically, copper-wired bus systems are used in the car environment. In the past 15 years, POF has replaced the electrical wiring in many types of car (see Figure 3). It was first introduced by BMW in the 7er series in 2001. Since then, not only high-class cars were equipped with POF, actually more than 200 types of volume cars benefit from the advantages of POF [4, 5]. The used bus is called Media Oriented Systems Transport (MOST), which is a multimedia network optimized for multimedia and infotainment applications. The bus was developed by the automotive industry. It works in three data rate levels with 25, 50 and 150 Mbit/s. MOST defines basically the physical interconnection between devices by using POF as a transport medium. Additionally, it specifies and standardizes a communication protocol to develop complete systems and applications to distribute multimedia content for the car.
\nMultimedia bus system (MOST-bus) with POF.
The replacement of the communication technique from copper wires to POF leads to lower weight. The low melting temperature of PMMA (95°C) still prevents the use of POF in the engine compartment. However, new types of fiber in the development that have higher glass transition temperature will allow the use of high-temperature POF in the engine compartment in the near future [4]. Another application in the car, where POF most likely will be used in the future, is as sensors for measuring various in-car pressures or forces. Additionally, sides emitting polymeric fibers are interesting devices for future applications for ambient lighting in the passenger cabin.
\nAnother sector where POF displaces the traditional communication medium is in-house communication [6, 7], although the possibilities of application are not confined to the inside of the house itself. In the future, POF can possibly displace copper cables for the so-called last mile between the last distribution box of the telecommunication company and the end consumer. Today, copper cables are the most significant bottleneck for high-speed Internet.
\n“Triple Play” is called the combination of IPTV, VoIP and the data Internet. The combination is currently introduced into the telecom market; therefore, high-speed connections are essential. It is highly expensive and bandwidth limiting to use Ethernet in-house system using copper components, thus the future will be FTTH, in combination with optical in-house wires of POF or GOF (see Figure 4).
\nIn-house communication with POF.
In this chapter, various transceivers, which can be used for data home cabling with optical polymer fibers, are examined with respect to their interoperability. Eight different devices are tested for their effective data rate over length-varying POF transmission distances. Furthermore, the results are compared with the manufacturer’s data regarding performance and the interoperability of all devices is checked.
\nThe Photonic Communications Lab at the Harz University works closely together with manufacturers of various POF components in several projects. From this cooperation, the question of the compatibility of POF devices from different manufacturers among one another has become increasingly important. All devices tested comply with the IEEE 802.3u guidelines for Fast Ethernet. Fast Ethernet is mainly used in local networks and allows data transmission at 100 Mbit/s.
\nTable 1 shows the tested media converters or switches with specifications from the manufacturer:
\nName | \nWavelength (nm) | \nTransmission length (m) | \nData transfer rate (Mbit/s) | \n
---|---|---|---|
Speedport OptoLAN | \n670 | \n30 | \n100 | \n
Diemount CS-116 | \n470 | \n70 | \n100 | \n
Rutenbeck wall socket | \n660 | \n70 | \n100 | \n
Rutenbeck socket switch | \n660 | \n50 | \n100 | \n
Media converter Rutenbeck | \n660 | \n50 | \n100 | \n
Switch OMS 126S-150 Homefibre | \n650 | \n50 | \n100 | \n
Switch CP8016 BSPCOM | \n650 | \n50 | \n250 | \n
Used POF-transceivers.
As can be seen in Table 1 and Figure 5 devices from various companies are examined. Starting with media converters of German manufacturers (Siemens, Diemount and Rutenbeck) to transceiver-switches from Homefibre (Austria) and BSPCOM (China).
\nA USB media converter from the company BSPCOM could not be considered for investigations for reasons of problems with the USB driver software for Windows (Figure 5).
\nTested media converter: Speedport, Diemount, BSPCOM, Rutenbeck and Homefibre.
All the devices tested, except the CS-116 from Diemount, operate at a wavelength in the visible red range. The device from Diemount transmits data at the wavelength of 470 nm in the visible blue range (see Figure 2).
\nIn the investigations of the POF devices, each existing one is combined with each, connected by a POF of 50 m length and put into operation. The measurements are carried out using a certification scheme developed in the Photonic Communications Lab of Harz University in accordance with the ETSI TS 105175–1 V1.1.1 (220010-01) standard, which establishes an in-house networking of the optical polymer fibers.
\nThe optical polymer fibers are wound up with the aid of two cylinders. These cylinders have different diameters and thus offer different bending radii (see Figure 6) in order to apply the typical application conditions of a typical LAN network distribution in an apartment.
\nSetup for testing typical laying of a POF with a length of 30 m in an apartment with 15 bends of different radii (in mm).
Several optical polymer fibers are wound onto this structure. These differ in length and outer cable diameter. However, all have a step index profile with a core diameter of 980/1000 μm. The cable diameter varies between 1.5 and 2.2 mm. The 2.2 mm fibers are being designed for simplex transmissions only. The 1.5 mm fibers are duplex fibers. The lengths of the optical polymer fibers are: 1, 15, 30 and 50 m.
\nIperf is a command line utility for measuring the performance of networks. Jperf is a graphical interface developed in Java for Jperf. This program is started on two PCs, one of which is the function of the server and the other is assigned to the client (see Figure 7). The server accepts connections on TCP port 5001. Data are transferred from the client to the server for the duration of the measurement. Thus, unidirectional data transmission always takes place.
\nMeasurement setup with Jperf (MC (media converter)—DUT.
Iperf offers different, adjustable parameters for throughput measurements. Examples of this are the selection of the transmission protocol (TCP/IP or UDP) as well as the modification of the measurement duration. In addition, the buffer size can be changed. The measurements are carried out in transmission control protocol (TCP) [8].
\nAt a transmission distance of only 1 m (back to back), all media converters and switches are working together with transmission speeds in the range of 90 Mbit/s (see Figures 8 and 9). However, in some combinations, the quality of the transmission rate is lower for this short distance than for a longer distance such as 30 or 50 m. Overdriving at the photodiode due to the excessive light intensity may cause this.
\nEffective measured data rates within one manufacturer.
Measured effective data rates with 15 m POF length between different manufacturers.
All the transceivers of the different manufacturers have been able to communicate with each other easily and also over the distances of 15 and 30 m, and all tests have been positive. The data rate fluctuates ±1–2 Mbit/s in the range of 92 Mbit/s. A 50 m transmission cannot be positively tested in combinations in which the Diemount CS-116 media converter is used as a client and with a blue transmit diode. This can be explained by the fact that the tolerance window of the photodiodes of the other devices is setup in the red range to this range by 650 nm. However, it should be noted that the light output up to 30 m was still intense enough to achieve a functionality of the two wavelengths without problems.
\nIn addition, the Speedport OptoLAN from Siemens is able to achieve 50 m transmission distances in almost all combinations. In general, it should be mentioned that the data rates reported by the manufacturers of 100 Mbit/s were not achieved by any system. On the other hand, all manufacturers did not provide a minimum data rate to be compared with the measurement results. The POF switch from BSPCOM from China shows the most stable transmission in all combinations and transmission lengths.
\nDuring the use of Jperf as a tool for recording the data rate, some points must be noted. On the one hand, higher transmission data values are always detected when the duration of the measurement is set to longer sampling values. This can be explained by the fact that the measuring interval is longer during a longer measuring period than in the case of a shorter measuring duration. Consequently, a mean value formation takes place. The reason is that the output format of Jperf of Mbit/s calculates large rounding errors. In addition, there is an error in the calculation of the average bandwidth over the whole measurement period by recalculation in Excel. The mean bandwidth was always larger than calculated externally. Therefore, the external calculated values are used in the evaluation.
\nAt present, the great potential of the POF is not available as the alternative techniques offer transmission rates up to 10 Gbit/s over copper and up to 40 Gbit/s over glass fibers in the network area. The WDM technique offers an approach to achieve these high data rates also in the POF range. A sketch of the basic principle is shown in Figure 10.
\nSchematic of the WDM over POF structure.
Wavelength division multiplex systems need two basic components of a multiplexer and a demultiplexer (see Figure 10). To realize a working DEMUX for POF, several preconditions must be fulfilled. The basic component is a mirror, which focuses a divergent light beam coming from the input fiber. The shape of this mirror must be a toric shape to prevent spherical aberrations [9, 10, 11].
\nTo separate the different incoming wavelength channels, a diffraction grating is used. This principle is illustrated in Figure 11. The light is split into different orders of diffraction. The first order is the important one to regain all information. There, the outgoing fibers with the different wavelengths channels must be arranged.
\nRowland setup of demultiplexer.
The development of the injection-molding process starts with the production of a master for the imprint of the entire component. This master is milled in micrometer precision by means of a diamond cutting process and created by the diamond turning process. Here, the PMMA material is processed directly. Both the moldings as well as the grid for wavelength separation can be made using this technique (see Figure 12). The last step is performed to validate the simulation results with the produced component.
\nIntegrated demultiplexer prototype.
For the injection-molding process, the production of the impression part is the most important factor. Due to the three-dimensional toric structure of the grating planar manufacturing methods like lithography, especially LIGA [a German acronym for Lithographie, Galvanoformung, Abformung (Lithography, Electroplating and Molding)] cannot be used. LIGA is used to manufacture planar spectrometers based on the glass fiber technology [12, 13, 14, 15]. In the present approach for using a grating as a WDM element, it is necessary to manufacture the three-dimensional grating with its fine line structure and blaze precisely. In particular, the microstructure of the grating and the exact shape of the toric surface require high precision. The blaze with the grating lines is a microstructure in the form of a sawtooth with a distance between the teeth of 2.5 μm. Figure 13 shows an enlarged 3D model of the grating. After analysis of other microtechnical machining processes to our knowledge, only the diamond turning meets the stringent requirements of the microstructured grating (Figure 14).
\nGrating of the demultiplexer.
Measurement results of the focal points for different wavelengths (405 nm 15.6°, 450 nm 17.8°, 520 nm 21.9° and 650 nm 26.0°).
The DEMUX elements must be manufactured in injection-molding technology. The capability of injection-molding technology for the cost-effective mass production of large volume and micrometer-accurate plastic components has made this technology the industrial standard production method for plastic parts. More and more high-quality optical components are produced with injection molding. With the aid of the injection molding, dimensionally stable and stress-free molded parts can be produced. In particular, the reduction of internal mechanical stress makes this technique ideal for optical mold components [12]. With this cost-effective production, the components for WDM can be made available via POF for a very wide application market. To further reduce the production costs, a self-adjustment of the individual optical components of the DEMUX such as fiber, grating, focusing mirror is necessary. This is why the various functions are combined in a molded part. However, this makes DEMUX technologically more difficult to implement, and therefore the individual process steps are discussed in detail.
\nIn the first step, a demonstrator was produced. In order to verify the concept of the demultiplexer and to compare the simulation results with the real setup, it is necessary to proceed step by step. For this reason, a special optomechanical design was chosen. Figure 15 shows the new design where a hemisphere at the output of the DEMUX represents the radius of the Rowland circle. This is shown in the cross-sectional view in Figure 16. The light reflected from the grating and emanating from the circle is focused on this radius. Therefore, the light is coupled into the center of the hemisphere, and the separated wavelengths can be detected on the surface of the hemispheres. This is illustrated in Figure 14. For detection, scanning of the surface is performed to determine the positions of the outgoing, separated light for each wavelength.
\n3D model of the DEMUX demonstrator.
Cross-section view of the DEMUX demonstrator.
Prior to the production of the DEMUX, some preliminary investigations have taken place to find the best suitable material for the demultiplexer. Therefore, both the processability of the material and the optical parameters had to be considered in detail. The injection-molding process was tested with a thick-walled mold. This test tool had the same shape as the final DEMUX, except for the grid. The test runs were carried out with an injection-molding machine from Babyplast 6-10P. This device was able to inject precisely small parts. Table 1 lists all the materials used for the study. Further, parameters such as the respective melt volume rate (MVR) and light transmittance (according to the manufacturer’s specification) are depicted. The test was additionally used to find the optimized injection-molding process parameters for the material.
\nIn addition, the optical quality of the polymer materials must be investigated. Therefore, a mold for injection-molding test plates was designed. The test plates had a thickness of 2 mm. The mold is used to make samples from each material listed in Table 2. The DIN EN ISO 13468–2 standard describes the measurement of the optical transmission of polymer materials. Therefore, the test plates are designed to meet this standard.
\nTransmission measurements were carried out with all test plates. The results are shown for 405 nm in Figure 17. It can be seen that both ZEONEX types and PMMA POQ62 show the highest value for the light transmission. PMMA POQ62 is a polymer grade with high purity of polymer granulates. The measurement is made at a wavelength of 405 nm because it is one of the wavelengths used for the WDM system.
\nTransmission of different material at 405 nm.
By using the injection-molding process, the manufacturing of the mold insert is the most important factor. Due to the three-dimensional toric structure of the grating planar manufacturing methods like lithography, especially LIGA cannot be used [15].
\nIn our case, however, the three-dimensional grating requires a different processing method. The microstructure of the grating and the exact shape of the toric surface require a particularly high precision of manufacture. The microstructure has the shape of a sawtooth with a distance between the teeth of 2.5 μm. Figure 13 shows an enlarged 3D model of the grating. An in-depth investigation of various processing methods has shown that only the diamond turning fulfills the high requirements of the production of the microstructural lattice. The diamond twisting technique is a special machining method using a single crystal diamond cutting tool. It is also possible to produce a surface with an optical quality at the edge of the optical component. It offers several advantages:
True three-dimensional contour generation.
Accuracy of one part in 106 with absolute accuracy of 1 part in 108 on a single axis for ideal conditions.
Surface finish of 5 nm Rz for a range of materials and as good as 1 nm Ra.
Ability to generate surfaces with variable aspect ratios and
Feature sizes that exceed the limits of optical microscopy [14, 15].
A metallization process was used to analyze the surface of the lattice. The surface was sputtered with a thin aluminum layer depicted in Figure 18. It is now possible to measure the shape of the surface with a white light interferometer and to examine the lattice structure under the scanning electron microscope (SEM). The metallized surface of the grating is shown in Figure 18. It can be seen that the structure on the left side has a dull and mat surface instead of the glossy residue of the surface. This is a first indication that the surface roughness in this part is higher and does not meet the requirements for the component precision. The first visual impression was then confirmed by the analysis under the SEM.
\nHigh-quality structures of the grating.
The cause of the degradation of the grating quality is the change in the strain as the milling tool passes the highest point in the center of the surface. It changes the way the force is exerted by a pushing movement on the surface. This results in a coarse structure on the other half of the surface. From the measurement of the structure size in Figure 19, a width of 2.55 μm can be determined, which is within the tolerances of the reference of 2.5 μm.
\nMetallized grating surface of the DEMUX.
In addition to the structural quality, the dimensions of the surface are also important for the functionality of the DEMUX and must be considered in detail. The shape of the radius of the toric surface was designed to focus the colored light beams on the Rowland circle. Therefore, it was analyzed using a white light interferometer (FRT MicroProf). The cross-section of the toric surface was measured. The measurement shows that the dimensions of the surface correspond to the tolerances of the DEMUX. An exception can be seen in the diameter in the x-axis, which is somewhat out of tolerance (Table 3).
\nName | \nType | \nMVR [cm3/10 min] | \nTransmission [%] | \n
---|---|---|---|
Plexiglas 6 N | \nPMMA | \n12 | \n92 | \n
Plexiglas POQ62 | \nPMMA | \n21 | \n92 | \n
Topas 5013 L-10 | \nCOC | \n48 | \n91.4 | \n
Topas 6013 M-07 | \nCOC | \n14 | \n91 | \n
ZEONEX F52R | \nCOP | \n22 | \n92 | \n
ZEONEX 350R | \nCOP | \n26 | \n92 | \n
Makrolon LED2245 | \nPC | \n35 | \n90 | \n
Injection-molding materials for MUX/DEMUX-element.
Dimension | \nMeasurement (mm) | \nReference (mm) | \n
---|---|---|
Diameter x-axis | \n15.869 | \n>16.000 ± 0.1 | \n
Diameter y-axis | \n15.887 | \n>15.170 ± 0.1 | \n
Height of grating | \n1.862 | \n1.872 ± 0.05 | \n
Measurement results of the DEMUX dimensions.
Several parameters have to be optimized in order to correct the manufacturing errors. This is performed in several iterations in close cooperation with the manufacturer. For example, the adjustment of the force applied to the surface was varied and optimized by the diamond tip. The next part with optimized parameters is now in production and is then analyzed in the same way to check the adjustments of the parameters.
\nIn order to measure the position of the focal points of the different separated wavelengths on the Rowland circuit, a special measurement setup was chosen. It uses a parallel kinematic precision alignment system to align a POF on the surface of the hemispheres. An input fiber firmly bonded to index matching is used to couple white light into the DEMUX, as shown in Figure 16. In this figure, it can be seen that the separated wavelengths are focused on a ring on the hemisphere. This ring is scanned by the fiber on the alignment system. The light from the scanning fiber is analyzed by using a spectrometer.
\nFrom the spectra along the Rowland ring, the location of the maxima of the wavelengths is determined. For the first component, the entire measurement was performed and compared with the simulation results. Four different wavelengths that were used to analyze the wavelength separation are as follows: 405, 450, 520 and 650 nm.
\nThe positions of the wavelengths measured by the setup are also depicted in Figure 14. In comparison to the simulation, a shift of the positions of 2,3° are found. Nevertheless, the separation of the wavelengths was measured and confirmed the functionality of the demultiplexer.
\nThe derivations to the simulation could be caused through the following reasons:
Derivation of the blaze angle of the sawtooth grating
Inhomogeneous structure of the grating
Manufacturing tolerances
These depend strongly on the precision of the manufacturing process. As mentioned in the previous section, the production of such complex structures on a toric surface is a major challenge. Therefore, the process parameters must be improved and optimized to fully meet the optical requirements of the demultiplexer component.
\nBesides developing low-IL cost-effective POF WDM components and fast POF WDM transmission systems, it is also important to allocate a unique set of WDM transmission channels in the visible spectrum to support WDM applications over SI-POF. To evaluate the applicability of a spectral grid to support visible spectrum WDM applications over SI-POF, the appropriate criteria were first established. Those criteria refer to:
Channel distribution with respect to the spectral attenuation of SI-POF;
Performances of different demultiplexing techniques;
Availability of laser diodes in the visible spectrum.
If ITU-T G.694.2 CWDM wavelength grid would be extended into the visible spectrum, 15 equidistant channels between 400 and 700 nm would be obtained, as shown in Figure 14. The parameters of the grid including the nominal central wavelengths are depicted with arrows in Figure 20.
\nExtension of CWDM wavelength grid into the visible spectrum and channel plans for 4-, 8-, 12- and 15-channel applications.
The channel spacing of 20 nm makes good utilization of the available spectral range. In the red window, the extension has a channel at 651 nm, which is very close to the attenuation minimum at 650 nm. The channel distribution also corresponds well to three other attenuation windows. The channels experiencing the highest attenuation are those at 611, 631, 671 and 691 nm. Those channels could be used for distances up to 20 m since they would experience approximately the same attenuation as 651 nm channel over 50 m, but lower intermodal dispersion. Good channel allocation, sufficient channel spacing, high channel count and good availability of the transmitters make the extension of CWDM grid very suitable to support WDM applications over SI-POF.
\nCurrently, commercially available POF transmission systems are able to fulfill the needs of IEEE 802.3 requirements with a data rate of 100 Mbit/s. The interoperability between the devices of the different manufacturers is also in a good condition.
\nTo realize higher bitrates WDM over POF will be an interesting application. We produced a DEMUX by injection molding.
\nThe realization of this DEMUX element for POF presents several challenges, in particular the microstructure of the grating on the three-dimensional surface. It is shown that it is possible to realize the structure size and the exact radius for the DEMUX with the current optimized production process. The high challenge of producing the blazed grating leads to some errors in the milling process, which still needs to be improved. This will be done in the future by optimizing the process parameters. The next parts will be produced and analyzed with the optimized parameters.
\nThis hopeful result shows that WDM applications over SI-POF with high Gbit/s transmission are a realistic aim for the next future. The technique will be able to extend the bandwidth in POF systems strongly. It seems to be possible to transmit 40 Gbit/s via 15 channels and a channel rate of 2,7 Gbit/s data rate with WDM over POF. This opens the range of POF applications to existing cloud centers and future in-house networks with to link length up to 100 m.
\nWe gratefully acknowledge the funding by the German Ministry of Education and Research (BMBF) under grant number 16 V0009 (HS Harz) /16 V0010 (TU BS). All injection molded parts are done with the support of the Institute of Micro and Sensor Systems at the Otto-von-Guericke University Magdeburg and Prof. Bertram Schmidt.
\nThe company was founded in Vienna in 2004 by Alex Lazinica and Vedran Kordic, two PhD students researching robotics. While completing our PhDs, we found it difficult to access the research we needed. So, we decided to create a new Open Access publisher. A better one, where researchers like us could find the information they needed easily. The result is IntechOpen, an Open Access publisher that puts the academic needs of the researchers before the business interests of publishers.
",metaTitle:"Our story",metaDescription:"The company was founded in Vienna in 2004 by Alex Lazinica and Vedran Kordic, two PhD students researching robotics. While completing our PhDs, we found it difficult to access the research we needed. So, we decided to create a new Open Access publisher. A better one, where researchers like us could find the information they needed easily. The result is IntechOpen, an Open Access publisher that puts the academic needs of the researchers before the business interests of publishers.",metaKeywords:null,canonicalURL:"/page/our-story",contentRaw:'[{"type":"htmlEditorComponent","content":"We started by publishing journals and books from the fields of science we were most familiar with - AI, robotics, manufacturing and operations research. Through our growing network of institutions and authors, we soon expanded into related fields like environmental engineering, nanotechnology, computer science, renewable energy and electrical engineering, Today, we are the world’s largest Open Access publisher of scientific research, with over 4,200 books and 54,000 scientific works including peer-reviewed content from more than 116,000 scientists spanning 161 countries. Our authors range from globally-renowned Nobel Prize winners to up-and-coming researchers at the cutting edge of scientific discovery.
\\n\\nIn the same year that IntechOpen was founded, we launched what was at the time the first ever Open Access, peer-reviewed journal in its field: the International Journal of Advanced Robotic Systems (IJARS).
\\n\\n2004
\\n\\n2005
\\n\\n2006
\\n\\n2008
\\n\\n2009
\\n\\n2010
\\n\\n2011
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\\n\\nWe started by publishing journals and books from the fields of science we were most familiar with - AI, robotics, manufacturing and operations research. Through our growing network of institutions and authors, we soon expanded into related fields like environmental engineering, nanotechnology, computer science, renewable energy and electrical engineering, Today, we are the world’s largest Open Access publisher of scientific research, with over 4,200 books and 54,000 scientific works including peer-reviewed content from more than 116,000 scientists spanning 161 countries. Our authors range from globally-renowned Nobel Prize winners to up-and-coming researchers at the cutting edge of scientific discovery.
\n\nIn the same year that IntechOpen was founded, we launched what was at the time the first ever Open Access, peer-reviewed journal in its field: the International Journal of Advanced Robotic Systems (IJARS).
\n\n2004
\n\n2005
\n\n2006
\n\n2008
\n\n2009
\n\n2010
\n\n2011
\n\n2012
\n\n2013
\n\n2014
\n\n2015
\n\n2016
\n\n2017
\n\n