Adaptation and Psychometric Properties of the German Version of the Dissociative Experience Scale

Transcription

1 Journal of Traumatic Stress, Vol. 11, No. 4, 1998 Brief Report Adaptation and Psychometric Properties of the German Version of the Dissociative Experience Scale Carsten Spitzer,1,6 Harald J. Freyberger,1 Rolf-Dieter Stieglitz,2 Eve B. Carlson,3 Gabriela Kuhn,4 Norbert Magdeburg,4 and Christof Kessler5 We introduce the 'Fragebogen zu Dissoziativen Symptomen' (FDS), a German adaptation of the Dissociative Experience Scale (DES) which was developed to screen for dissociation within an ICD-10 framework. In addition to the original 28 DES items, the FDS contains 16 items covering dissociative phenomena included in the ICD-10, particularly pseudoneurological conversion symptoms. The psychometric properties of the FDS were studied in 927 clinical and nonclinical subjects from different diagnostic groups and compared to results of American studies. The scale had good test-retest reliability of.88, high internal consistency (split-half =.90, Cronbach's alpha =.94) and good construct validity. These results indicate that the FDS may be a valuable screen for dissociative psychopathology in German-speaking countries. KEY WORDS: dissociation; conversion; Dissociative Experience Scale; screening measure; psychometric properties. Clinical interest and research in Europe and particularly in Germany in the field of dissociation and traumatic stress are lagging far behind North 1Department of Psychiatry and Psychotherapy, Ernst-Moritz-Arndt University, Greifswald, Section Stralsund, Stralsund, Germany. 2Department of Psychiatry and Psychotherapy, Albert-Ludwigs-University, Freiburg, Germany. 3Clinical Psychology Associates, Delevan, Wisconsin. 4Department of Psychiatry and Psychotherapy, Medical University, Lubeck, Germany. 5Department of Neurology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany. 6To whom correspondence should be addressed to Department of Psychiatry and Psychotherapy, Ernst-Moritz-Arndt University, Section Stralsund, Rostocker Chaussee 70, D-18437, Stralsund, Germany /98/ $15.00/1 C 1998 International Society for Traumatic Stress Studies

2 800 Spitzer et al. America (Spitzer, Freyberger, & Kessler, 1996; Vanderlinden, Van der Hart, & Varga, 1996). There are several major reasons for this, one being a considerable skepticism towards the diagnosis of dissociative identity disorder (DID; Merskey, 1992). The second reason refers to the divergent classification of the dissociative disorders and posttraumatic stress disorder (PTSD) in the DSM-IV (American Psychiatric Association [APA], 1994), which is used in North America, and the ICD-10 (World Health Organization, 1991), which is in wide clinical and research use in Germany (Garcia, 1990). In the DSM-IV PTSD is viewed as an anxiety disorder while it is classified under the adjustment disorders in the ICD-10. Another main difference is the classification of conversion disorders which are subsumed under the somatoform disorders in the DSM-IV In contrast, the ICD-10 combines conversion and dissociative disorders into one diagnostic category. This can partly be attributed to the fact that the theories of both dissociation and conversion are closely linked to the concept of hysteria (Kihlstrom, 1994). It was also argued that conversion and dissociation are based on the same psychological mechanism (Nemiah, 1993). Supporting this line of argumentation, several empirical studies indicated that conversion symptoms and disorders are frequently found in dissociative disorders (reviewed by Cardena & Spiegel, 1996). Conversely, dissociation and traumatic stress are prominent in conversion disorder patients, particularly in pseudoseizure subjects (Bowman & Markand, 1996). Moreover, a lack of screening and diagnostic instruments might also be responsible for the deficient attention being paid to dissociation and traumatic stress in Germany (Spitzer et al., 1996). Recently, a European dissociation questionnaire was developed to suit the sociocultural situation (Vanderlinden, Van Dyck, Vandereycken, Vertommen, & Verkes, 1993). However, for the German-speaking countries, this measure has the major drawback of conforming with the DSM concept of dissociation and consequently does not cover conversion symptoms. Because multinational research on dissociation and traumatic stress is in need of comparable research tools, our objectives were to introduce an internationally well-established screen for dissociative psychopathology and adapt it for German-speaking countries, thus allowing its use within the ICD-10 framework. We chose the Dissociative Experience Scale (DES; Bernstein & Putnam, 1986) because it is one of the major tools used in research on dissociation and traumatic stress (Carlson & Putnam, 1993). For the DES, different studies focused on the reliability and validity (reviewed by Carlson & Putnam, 1993; van Ijzendoorn & Schuengel, 1996). With respect to construct validity, we expected patients with dissociative and conversion disorders to score high on the instrument, whereas other diag-

3 Dissociative Experience Scale German Version 801 nostic samples would yield low scores. Assuming that dissociation reflects a distinct form of psychopathology, we predicted an association with other dimensions of psychopathology. We attempted to replicate the psychometric investigations conducted with the DES using the German version. Participants Method A total of 927 clinical and nonclinical participants from nine different diagnostic groups were recruited. General exclusion criteria were cognitive impairment and alcohol abuse and/or drug abuse (except for the sample of alcoholics). The number of participants analyzed by diagnostic group, age, and sex are shown in Table 1. A consecutive series of 211 psychiatric inpatients taking part in the psychotherapy program of our university department were screened for dissociative and depersonalization disorders by an experienced psychiatrist with expertise in the area of dissociation. Screening was performed by means of an intensive clinical interview. The interviewer was blind to the FDS scores in all cases. Fifty nine patients (28%) met diagnostic criteria for dissociative or depersonalization disorders according to the ICD-10. Of these 59 patients, 28 (47%) suffered from dissociative amnesia, 19 (32%) were diagnosed as having depersonalization disorder, and 12 (20%) were classified as having dissociative disorders not otherwise specified (DDNOS). The ICD-10 diagnoses of the remaining 152 patients without any dissociative disorders are presented in Table 2. Table 1. Age and Sex Characteristics of Participants as a Function of Diagnostic Group Sample Group Size M Age SD Number of Females N % Dissociative disorders Psychiatric patients Nonclinical controls Students Surgical patients Alcoholics Schizophrenics Neurological patients Conversion disorders Total

4 802 Spitzer et al. F32 F33 F34 F40 F41 F42 F43 F45 F48 F50 F60 Table 2. Distribution of Clinical Main and Second Diagnoses According to the ICD-10 of 152 Psychiatric Patients Without a Dissociative Disorder ICD-10 code Depressive episode Recurrent depressive episode Persistent depressive disorder Phobic disorder Other anxiety disorder Obsessive-compulsive disorder Adjustment disorder Somatoform disorder Other neurotic disorder Eating disorder Personality disorder Main diagnosis N(%) 17 (11) 8(5) 14(9) 8(5) 21 (14) 2(1) 40 (26) 11(7) 14(9) 17 (11) Second diagnosis N(%) 3(2) 2(1) 1(1) 1 (1) 6(4) 1(1) 3(2) 5(3) 3(2) 6(4) 24 (16) Nonclinical controls were a convenience sample of colleagues, relatives and friends of the researchers. The student sample was comprised of individuals attending lectures in psychiatry at the Medical University of Lubeck, Germany. Of these, a subgroup of 56 students completed the questionnaire again after an interval of 14 days. Surgical patients were recruited from a medical trauma ward and had presented for treatment with orthopedic fractures. The sample of alcoholics had undergone a withdrawal therapy program at our university department. The schizophrenics were only included when severe conceptual disorganization was ruled out. The neurological inpatients suffering from definite organic diseases (e.g., multiple sclerosis) were randomly selected. Conversion disorders in neurological patients were only diagnosed after intensive diagnostic procedures failed to identify an organic cause for the presented symptoms. Patients were independently assessed by a neurologist and afterwards by a psychiatrist to confirm the diagnosis of conversion. Three hundred ninety patients of the different clinical samples also completed the SCL-90. All participants gave informed consent. Instruments Dissociative Experience Scale. The DES (Bernstein & Putnam, 1986; Carlson & Putnam, 1993) is a 28-item self-report measure of the frequency of dissociative experiences of varying severity. To answer DES questions subjects circle the percentage of time (given in 10% increments ranging from 0 to 100) that they have the experience described. The total DES score is the mean of all item scores.

5 Dissociative Experience Scale German Version 803 The procedure for translation of the DES into German began with two independent translations of the measure, one by a bilingual person who was unfamiliar with the concept of dissociation and the second one by the corresponding author. These two translations were discussed, improved and assembled into one version. In the next step, a back-translation of this version was performed by a native English-speaking person not involved in the translation into German. This back-translation was compared to the original DES and changes of the German translation were made when necessary. Then 16 items were added to the scale to assess additional dissociative symptoms from the ICD-10. These ICD-10 subscale items largely cover pseudoneurological conversion symptoms. They were written with similar wording and format as the original DES items. These additional items can be provided upon request. A final version was established which was named "Fragebogen zu Dissoziativen Symptomen" (FDS). The FDS is administered and scored in the same way as the DES. Symptom Check List-90. The revised version of the SCL-90 (Derogatis, 1983) is a 90-item self-report inventory widely used to measure current psychopathological symptoms. In addition to a global rating (Global Severity Index), nine syndrome scores can be calculated: somatization, obsessional compulsion, interpersonal sensitivity, depression, anxiety, anger-hostility, phobic anxiety, paranoid ideation, and psychoticism. Subjects are required to rate responses on a 5-point scale. Scores are calculated as the mean response on the relevant items with high scores reflecting a severe degree of psychopathology. Evidence supporting the reliability and validity of the German version of the SCL-90 is similar to evidence likewise supporting the original version (Derogatis, 1986). Data Analyses The statistical analyses were computed using the "Statistical Package for the Social Sciences" (SPSS PC+, version 4.0). Reliability was examined by calculating the test-retest coefficient using Spearman rank-order correlations, the split-half coefficient and Cronbach's alpha. For comparison of the different diagnostic groups, analyses of variance (ANOVA) were performed followed by post hoc pairwise comparisons according to Bonferroni's modified least-significant difference method. Concurrent validity was assessed by computing Spearman rank-order correlations. Significance level was established at p <.05.

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7 Dissociative Experience Scale German Version 805 Results Reliability For the FDS and the DES (subset of 28 FDS items), the test-retest coefficients were.88 and.86, respectively, in the subsample of 56 students. Split-half reliability was.90 for the FDS and.88 for the DES in the total study sample. Cronbach's alphas were.94 and.91, respectively. Criterion-Related Validity Figure 1 shows the mean FDS and DES scores of the different study samples. The FDS score significantly discriminated between different diagnostic groups as computed with analyses of variance yielding an F(8, 918) = 33.27, p <.001. The comparable result for the DES was F(8, 918) = 24.81, p <.001. Post hoc pairwise comparisons revealed that the schizophrenic, conversion and dissociative disorder groups, while not differing significantly from each other, each significantly exceeded all other groups. Moreover, the nonclinical controls scored lower than psychiatric patients and students reaching statistical significance. The remaining diagnostic groups did not differ significantly on the FDS and DES, respectively. Concurrent Validity Correlation coefficients (n = 390) of the FDS and the DES with the SCL-90 were.34 and.26 for somatization,.43 for obsessional compulsion,.40 and.42 for interpersonal sensitivity,.34 for depression,.41 and.37 for anxiety,.38 and,40 for hostility,.43 and.40 for phobic anxiety,.39 and.41 for paranoid ideation, and.44 for psychoticism. The correlations of the Global Severity Index with the DES and FDS, respectively, were.57 and.59. All correlation coefficients reached a significance level of p <.001. The 16 additional items of the German version were positively correlated with the 28 items of the original version (r =.66; p <.001; n = 927). Discussion In summary, the German adaptation of the DES has good test-retest and split-half reliability and is internally consistent. There is evidence for

8 806 Spitzer et al. good criterion-related validity, in that item scores differentiate between different diagnostic groups. However, generalizability of our findings is limited because we used the ICD-10 for classification in contrast to the large majority of studies on the DES, which used DSM diagnostic criteria and thus diagnostic groups might not be totally equivalent. Another methodological problem concerns the nonclinical controls who were not sampled systematically to represent the general population. However, apart from one study (Ross, Joshi, & Currie, 1990) all studies presenting DES scores of nonclinical controls failed to show that their samples were representative of the general population (Carlson & Putnam, 1993; van Ijzendoorn & Schuengel, 1996). Finally, our investigation did not include PTSD and DID patients which might limit generalizability of our results, too. Notwithstanding these caveats, the FDS has similarly good to excellent psychometric properties as the DES. For a subgroup of 56 students we found a test-retest coefficient similar to the coefficients reported for the DES in student samples (van Ijzendoorn & Schuengel, 1996). Split-half reliability in our study nearly matched results for the DES (Bernstein & Putnam, 1986; Pitblado & Sanders, 1991). For our investigation, Cronbach's alpha was almost identical to those reported in the majority of studies on the DES (van Ijzendoorn & Schuengel, 1996). The criterion-related validity of the DES is represented by its ability to differentiate among different diagnostic groups (Carlson & Putnam, 1993; van Ijzendoorn & Schuengel, 1996). The FDS discriminates among patients with dissociative disorders or conversion disorders, psychiatric patients without any dissociative disorders, and non-clinical subjects (see Figure 1). This is consistent with findings reported for the DES (Bernstein & Putnam, 1986; Ross, Norton, & Anderson, 1988; Carlson & Putnam, 1993). However, it is noteworthy that DES mean scores of patients with a dissociative disorder are much lower than those reported previously (Carlson & Putnam, 1993; van Ijzendoorn & Schuengel, 1996). Apart from the general methodological limitations discussed above, it might also be that the majority of participants in our dissociative disorder group were moderate dissociators while only a very small proportion were high dissociators. In fact, none of the subjects in our dissociative disorder group were given the diagnosis of DID, which is generally associated with very high dissociation scores (Carlson et al, 1993; Putnam et al., 1996). It was also found that some patients with non-did-dissociative disorders score only moderately high on the DES. For example, approximately half of the subjects with non-did-dissociative disorders in a large multi-center study were moderate dissociators (Putnam et al., 1996). Their average score is comparable to the one in our sample of patients with non-did-dissociative disorders.

9 Dissociative Experience Scale German Version 807 Interestingly, the schizophrenics in our study scored nearly as high as patients with dissociative or conversion disorders which is in contrast to previous reports (Carlson et al., 1993). This might be due to schizophrenics with a clinically predominant positive syndrome who have significantly higher scores than those with a negative syndrome as was demonstrated recently (Spitzer, Haug, & Freyberger, 1997). However, this finding calls into question whether the FDS is able to differentiate between schizophrenics and dissociative disorder patients. A recent taxometric analysis of the DES, however, found evidence for both dimensional (or nonpathological) and typological (or pathological) dissociative experiences (Waller, Putnam, & Carlson, 1996). It was suggested that a taxonic model may be better suited for characterizing pathological dissociative symptoms. Such a taxometric approach may be useful in differentiating schizophrenic and dissociative patients with the FDS. Further evidence for construct validity of the FDS relates to the moderate, but significant correlations with SCL-90 subscales. They were lower than SCL-90 correlations reported for the DES in a student sample (Norton, Ross, & Novotny, 1990). These conflicting findings might be due to the different samples. Our results indicate that the FDS measures a construct which is related to but distinct from other dimensions of psychopathology. Adaptation of the DES for the German-speaking countries implied an extension to make it compatible with the ICD-10 by adding items covering conversion symptoms. Our results suggest that this extension did not influence the reliability of the scale. However, the evidence for the validity of these additional items is limited and needs to be established by future studies. Nevertheless, the high correlation of the 16 additional items with the 28 original items may indicate an association between conversion and dissociation. Corresponding to this, in our study conversion disorder patients scored only slightly lower than dissociative disorder subjects. This result is consistent with past studies reporting high dissociation scores in pseudoseizure patients (Bowman & Markand, 1996). This is one reason why reclassification of conversion seizures with dissociative disorders should be considered (Bowman & Markand, 1996). In line with others (Nemiah, 1993), we even suggest to generally classify conversion disorders with the dissociative disorders. This has been accomplished in the ICD-10 and there seems to be enough evidence to justify a parallel development in the DSM, thus increasing the compatibility of the two systems. In conclusion, the FDS might be a reliable and valid screen for dissociative psychopathology for the German-speaking countries, which can also be used within the ICD-10 framework. However, our first promising

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11 Dissociative Experience Scale German Version 809 Vanderlinden, J., Van der Hart, O., & Varga, K. (1996). European studies of dissociation. In L.K. Michelson & W.J. Ray (Eds.), Handbook of dissociation: Theoretical, empirical, and clinical perspectives (pp ). New York: Plenum Press. Vanderlinden, J., Van Dyck, R., Vandereycken, W., Vertommen, H., & Verkes, J.R. (1993). The Dissociation Questionnaire (DIS-Q). Development and characteristics of a new self-report questionnaire. Clinical Psychology and Psychotherapy, 1, Van Ijzendoorn, M.H., & Schuengel, C. (1996). The measurement of dissociation in normal and clinical populations: Meta-analytic validation of the Dissociative Experience Scale (DES). Clinical Psychology Review, 16, Waller, N.G., Putnam F.W., & Carlson E.B. (1996). Types of dissociation and dissociative types: A taxometric analysis of dissociative experiences. Psychological Methods, 1, World Health Organization (1991). Tenth Revision of the International Classification of Diseases, Chapter V (F): Mental and Behavioural Disorders, Clinical Descriptions and Diagnostic Guidelines. Geneva: Author.

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