Journal of Traumatic Stress Disorders & Treatment ISSN: 2324-8947

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Research Article, J Trauma Stress Disor Treat Vol: 2 Issue: 2

Preliminary Investigation of the Reliability and Validity of the German Version of the State Scale of Dissociation (SSD)

Mueller-Pfeiffer C1,2,3* and Wittmann L1,4
1University Hospital of Zurich, Switzerland
2Psychiatric Services of the County of St. Gallen-North, Switzerland
3Massachusetts General Hospital and Harvard Medical School, Boston MA, USA
4International Psychoanalytic University (IPU), Berlin, Germany
Corresponding author : Christoph Mueller-Pfeiffer
Department of Psychiatry and Psychotherapy, University Hospital Zurich, Culmannstrasse 8, 8091 Zurich, Switzerland
Tel:
+41-44-255-52-80; Fax: +41-44-255-44-08
E-mail: [email protected]
Received: March 08, 2013 Accepted: April 12, 2013 Published: April 18, 2013
Citation: Mueller-Pfeiffer C, Wittmann L (2013) Preliminary Investigation of the Reliability and Validity of the German Version of the State Scale of Dissociation (SSD). J Trauma Stress Disor Treat 2:2. doi:10.4172/2324-8947.1000106

Abstract

Preliminary Investigation of the Reliability and Validity of the German Version of the State Scale of Dissociation (SSD)

According to a new definition proposed by Spiegel and colleagues for DSM-V, dissociation is a “disruption of and/or discontinuity in the normal, subjective integration of one or more aspects of psychological functioning, including - but not limited to - memory, identity, consciousness, perception, and motor control. In essence, aspects of psychobiological functioning that should be associated, coordinated, and/or linked are not… Dissociative symptoms are characterized by (a) unbidden and unpleasant intrusions into awareness and behavior, with accompanying losses of continuity in subjective experience: (i.e., ‘positive’ dissociative symptoms); and/or (b) an inability to access information or to control mental functions that normally are readily amenable to access or control: (i.e., ‘negative’ dissociative symptoms’)”.

 

Keywords: Dissociative disorders; State dissociation; Self-rating scale; Outpatients; Day care-patients; Validity; State scale of dissociation; Multidimensional inventory of dissociation

Keywords

Dissociative disorders; State dissociation; Self-rating scale; Outpatients; Day care-patients; Validity; State scale of dissociation; Multidimensional inventory of dissociation

Introduction

According to a new definition proposed by Spiegel and colleagues for DSM-V, dissociation is a “disruption of and/or discontinuity in the normal, subjective integration of one or more aspects of psychological functioning, including - but not limited to - memory, identity, consciousness, perception, and motor control. In essence, aspects of psychobiological functioning that should be associated, coordinated, and/or linked are not… Dissociative symptoms are characterized by (a) unbidden and unpleasant intrusions into awareness and behavior, with accompanying losses of continuity in subjective experience: (i.e., ‘positive’ dissociative symptoms); and/or (b) an inability to access information or to control mental functions that normally are readily amenable to access or control: (i.e., ‘negative’ dissociative symptoms’)” [1].
Dissociation is the hallmark symptom of dissociative disorders (DDs), but can also occur in the context of non-DDs, e.g. anxiety disorders, affective disorders and borderline personality disorder [2]. Although an established etiology of dissociation is still lacking, most authors agree that there is a link between DDs/dissociation and exposure to traumatic events [3]. Trait dissociation, which refers to relatively consistently expressed dissociative symptoms within individuals over the span of time [4], is commonly measured using structured interviews, such as the Structured Clinical Interview for DSM-IV Dissociative Disorders – Revised (SCID-D-R) [5], as well as a variety of self-rating scales [6]. These instruments typically assess the frequency of dissociative symptoms in daily life, as a trait. In contrast, there are very few scales available that assess dissociative experiences at the time of the assessment, i.e., as a state. The assessment of dissociative state is relevant to studies investigating psychopharmacological or psychotherapeutic interventions, or physiological and neural correlates of dissociative symptoms.
A widely used instrument that measures dissociative states is the Clinician-Administered Dissociative States Scale (CADSS) [7], a 27- item scale with 19 self-rated items and 8 observer-rated items that assess three dimensions of dissociation: amnesia, depersonalization and derealization. No validated German adaptation of the original American version is available yet. The 22-item Dissociation-Tension Scale acute (DSS-acute), a German self-report scale, was developed for assessing five dimensions of dissociation: amnesia, depersonalization, derealization, absorption, and somatoform dissociation [8]. Internal consistency of the DSS-acute is high (Cronbach’s alpha = .93 for the total score; Guttmann’s split-half reliability coefficient = .93) and the scale discriminates well between patients with borderline personality disorder and patients with anxiety disorders, major depression, and schizophrenia, as well as individuals without a mental disorder. Principal components factor analysis has provided only limited support for the five factors; consequently, the authors have recommended using the DSS-acute total score. Additional limitations of the DSS-acute include that it does not cover all empirically-derived dimensions of dissociation, e.g., identity disturbances [9], and that no cross-cultural adaption is available. The State Scale of Dissociation [10] addresses some of these limitations. The SSD is a comprehensive, 56-item self-report scale that captures dissociative states in seven dimensions: amnesia, depersonalization, derealization, hypermnesia/ flashbacks, conversion, identity confusion, and identity alteration. These dimensions were developed by the original authors according to available evidence regarding distinct types of pathological dissociation. The present work tested the psychometric properties of a German translation of the SSD.

Materials and Methods

Subjects and procedure
Data were gathered within a larger study investigating the relationship between DDs and functional impairment [11] and the longitudinal course of DDs. Consecutive subjects between 18 and 65 years with sufficient fluency in the German language and in treatment for three or more sessions between 1/2009 to 12/2010 were eligible for the present study. Subjects were recruited from two public psychiatric outpatients units, a private practice, and two psychiatric day care units located in the Counties of St. Gallen or Zurich, Switzerland. The study protocol was approved by the institutional review board of the County of St. Gallen, Switzerland. All subjects provided written informed consent.
Measurements
Current diagnoses were ascertained with the Structured Clinical Interview for DSM-IV Axis I Disorders [12] and the SCID-D-R [5,13]. Inter-rater reliability for the five DSM-IV DD diagnoses, as determined from the SCID-D-R, was high in this study (Fleiss’ kappa = .9, 95% CI = .73 – 1.00, n = 84).
The English version of the SSD has demonstrated high internal consistency (Cronbach’s alpha between .82 and .97 for the total and subscale scores), adequate to good construct validity (Spearman rank correlations rs between .43 and .81 for various diagnostic groups between the SSD and the Dissociative Experiences Scale [14] scores), good concurrent validity (good differentiation between patients with versus without a dissociative disorder), and sensitivity to change [10]. The SSD asks for dissociative experiences “right now”. The 56 items are rated on 10-point scales ranging from 0 (“not at all”) to 9 (“very much so”) and then the item scores are averaged to produce a total mean score. The SSD was translated from English to German and then back translated from German to English. Both translation processes were carried out by native speakers of the target language who possess excellent knowledge of the source language. Following the original procedure for evaluating sensitivity to change in the English version of the SSD [10], the scale was administered at the beginning and end of a test session, which lasted on average 64 (SD = 44) min and consisted of completing a series of questionnaires that measured dissociative and non-dissociative symptomatology. The rationale for this procedure is the assumption that cognitive activity associated with completing the questionnaires serves as a grounding activity, which is expected to decrease state dissociation.
Trait dissociation was assessed using the Multidimensional Inventory of Dissociation (MID) [9,15]. The MID is a comprehensive scale with 218 items (168 dissociation items, 50 validity items) that measures pathological dissociation across six general dissociative symptoms (i.e., ‘memory problems’, ‘depersonalization’, ‘derealization’, ‘flashbacks’, ‘somatic symptoms’, ‘trance’), 11 consciously experienced intrusions from a dissociated self-state (e.g., child voices), and six fully-dissociated activities of another self-state (e.g., fugue episodes). The MID also provides categorical diagnoses (i.e., dissociative identity disorder, dissociative disorder not otherwise specified, posttraumatic stress disorder, and borderline personality disorder). The items are rated on an 11-point scale that ranges from 0 (“never”) to 10 (“always”). The scale provides a summary score between 0 and 100 by averaging the 168 dissociation items scores and multiplying by 10. The MID has demonstrated good reliability and validity [15]. Preliminary data [16] suggest sound psychometric properties of the German version of the MID (Cronbach’s alphas between .69 and .94) and good differentiation between patients with versus without a DD.
Data analysis
Statistical analyses were performed with IBM SPSS Statistics 19. All tests were two-tailed and used a significance level of p < .05. In order to test the reliability of the German SSD, Cronbach’s alpha was calculated for SSD total and subscale scores. Split-half reliabilities were also calculated for the total score (Guttman and Spearman-Brown). Reliabilities at the item and subscale levels were further assessed by discrimination indices (item-subscale, item-total, and subscale-total Pearson correlations). In order to assess concurrent validity, mean SSD scores of subjects with and without a DD were compared by an independent sample t-test. For quantification of convergent validity of the German SSD, Spearman rank correlations (rs) were calculated between SSD subscale scores (obtained from the SSD administered at the beginning of the test session) and their corresponding MID subscale scores. Discriminant validity was investigated by means of Spearman rank correlations between SSD subscales and noncorresponding MID subscales. Sensitivity to change was investigated by a repeated measures analysis of variance testing the effects of time (beginning versus end of the test session) and diagnostic group (presence versus absence of a DD) as well as their interaction on SSD total scores.

Results

Of the 117 participants, 27 (23.1%) received a DD diagnosis according to SCID-D-R: 1 dissociative fugue (3.7%), 10 dissociative identity disorder (37.0%), 6 depersonalisation disorder (22.2%), and 10 dissociative disorder not otherwise specified (37.0%). Sociodemographic and psychopathological characteristics for total sample and subsamples is presented in Table 1. Mean SSD total score for all subjects was 1.7 (SD = 1.8), mean MID total score was 15.8 (SD = 16.0). Concurrent validity was supported by significantly higher mean SSD total scores of DD subjects (M = 2.8, SD = 1.9, 95% CI [2.1, 3.5]) versus non-DD subjects (M = 1.4, SD = 1.6, 95% CI [1.1, 1.7]; t (115) = -3.91, p < .001). Internal consistency of the German SSD scale and subscales was excellent as indicated by high Cronbach’s alpha coefficients (for total score = .98; for subscale scores between .87 and .94) and split-half reliability coefficients (Guttmann = .89; Spearman- Brown equal length = .91). All item-subscale correlations were ≥ .59, and no item-total correlation was < .42. Subscale-total correlations ranged between r = .76 and r = .91 (all p < .001). Spearman’s rank correlations between corresponding SSD and MID subscale scores were high (Table 2). SSD derealization was more strongly correlated with MID derealization than with other MID subscales. SSD identity confusion was more strongly correlated with MID partially dissociated intrusions than with other MID subscales. Significant correlations were also observed between non-corresponding SSD and MID subscales. SSD scores decreased from the beginning of the test session to the end of the session (session duration: M = 64.3, SD = 44.2 minutes) in DD (pre: M = 2.8, SD = 1.9; post: M = 2.3, SD = 2.1) as well as in non-DD (pre: M = 1.4, SD = 1.6; post: M = 0.8, SD = 1.2) subjects, as revealed in significant main effects for time (F(1, 116) = 31.1, p < .001) and diagnostic group (F(1, 116) = 20.3, p < .001) in the absence of a significant interaction effect (F(1, 116) = 0.35, p = .555).
Table 1: Sociodemographics and Axis I Diagnoses for 117 Psychiatric Patients with and without a Dissociative Disorder.
Table 2: Correlation between State Scale of Dissociation (SSD) and Multidimensional Inventory of Dissociation (MID) Total and Subscale Scores in 117 Psychiatric Patients.

Discussion

The Cronbach’s alpha (≥ .87) and split-half reliability coefficients (≥ .89) observed for the German translation of the SSD were similar to those obtained with the original English version [≥ .82 and ≥ .92, respectively] [10], suggesting comparable reliabilities of the two versions. As was observed for the English version of the SSD, we found significantly higher mean SSD total scores in DD subjects versus non-DD subjects. However, DD subjects in this study reported substantially lower SSD scores (M = 2.8) than DD subjects in the Kruger study (M = 4.33). This discrepancy could be explained by the higher proportion of subjects with a depersonalization disorder in our study, who usually report lower dissociation levels than subjects with a dissociative identity disorder or dissociative disorder not otherwise specified [17]. It is also possible that treatment history differed between the two study samples. Strong correlations of the SSD subscales with corresponding MID subscales suggests good convergent validity. On the other hand, significant correlations between non-corresponding subscales of the SSD and MID suggest limited discriminant validity at the subscale level. However, it is important to keep in mind that the MID measures trait dissociation, therefore further examination of convergent and discriminant validity using a state measure of dissociation is needed for the German SSD. Future studies should also investigate the factor structure of state and trait dissociation.
SSD scores decreased in response to a cognitive activity, i.e., completing of self-rating questionnaires, replicating similar results by Kruger et al. This supports the use of the German SSD for measuring short-term changes in dissociative intensity in frequent assessments. Shorter scales such as the DSS-4 [18], a valid and reliable short version of the DSS-acute, might be more suitable for very rapid changes such as in experimental studies.
Limitations of this study are the relatively small samples sizes, the use of a convenience sample, and the lack of a comparison group of subjects without a mental disorder. Moreover, because data were gathered within a larger, longitudinal study, Axis I diagnoses were ascertained six months prior to administering the SSD and MID. Further research is needed to determine how responding to the many items of the SSD might influence one’s current dissociative state. This might be tested by modifying SSD instructions so as to focus on one’s state just prior to answering the questions rather than the state right now. Because administration of a test session might have only weak effects on state dissociation, sensitivity to change of the SSD might be investigated in future studies by applying more straight-forward interventions for eliciting or attenuating acute dissociative states, e.g., a stress test [19], or body-oriented grounding techniques [20].
The German adapted SSD showed good to excellent reliability, good concurrent validity, satisfied convergent validity, and was sensitive to change. We conclude that the German translation of the SSD scale is appropriate for assessing state dissociation in German psychiatric populations. The proposed factor structure of the German SSD should be tested in future studies using larger samples.

Acknowledgment

The study was funded by the Center of Education and Research (COEUR), Psychiatric Services of the County of St. Gallen-North, Switzerland and the Fritz Rohrer Fonds, Zurich, Switzerland.

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