The state scale of dissociation : development, psychometric validation, and application in a study of concurrent electro-encephalographic correlates
The distinction between state and trait dissociation informed the development and\ud psychometric validation of the State Scale of Dissociation (SSD) and the study of\ud concurrent electro-encephalographic (EEG) correlates of experimentally induced\ud dissociative states.\ud Existing scales measure trait dissociation. The need for a state scale was\ud addressed by the development and testing of a present-state, self-report measure.\ud Fifty-eight preliminary items were sorted into 7 subscales: derealisation,\ud depersonalisation, identity confusion, identity alteration, conversion, amnesia, and\ud hypermnesia. A revised 56-item SSD was administered with other psychiatric scales\ud (DES, BDI, BAI, SCI-PANSS) to patients with DSM-IV major depressive disorder\ud (n=19), schizophrenia (n=18), alcohol withdrawal (n=20), dissociative disorders\ud (n=10), and controls (n=63). The SSD was demonstrated to be a valid and reliable\ud measure of severity, and changes in severity, of dissociation at the time of its\ud completion. Discriminant validity, content, concurrent, predictive, internal criterionrelated,\ud internal construct, and convergent validities were confirmed statistically by\ud factor analysis, Spearman's rho correlations, confidence intervals, predictive analysis,\ud and parametric and non-parametric comparisons of dependent and independent\ud samples. It showed high internal consistency (Cronbach's alpha = 0.97) and high splithalf\ud reliability (Guttman coefficient = 0.92). The conversion subscale clustered with\ud the other subscales into one general factor on factor analysis and did not support its\ud segregation from dissociative disorders in DSM-IV.\ud State characteristics of dissociation were also examined in 11 patients with\ud complex partial epilepsy. The relationship between concurrent EEG and\ud experimentally induced dissociative states was examined by repeated SSD and\ud baseline DES measurements after spectral analysis of EEG. Canonical analysis\ud demonstrated significant SSD-EEG correlations. Amnesia, identity alteration, and\ud identity confusion correlated with theta, frontal delta, and fast wave EEG activity\ud respectively.\ud The SSD now allows for further investigation of the suggested state\ud continuum of severity and trait continuum of frequency of dissociation in more\ud comprehensive studies of concurrent neurobiological correlates.