A study of somatization disorder in a community population utilizing grade of membership analysis.

A new multivariate analytical technique for the analysis of medical classification, Grade of Membership analysis, is utilized to examine somatization disorder in a community population. The authors examine whether somatic symptoms will cluster into a clinical syndrome resembling somatization disorder, as defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM-III), if no prior assumptions are made about the inter-relationship of somatic symptoms or their clustering into clinical syndromes. Using respondents in the US National Institute of Mental Health Epidemiologic Catchment Area project of the Piedmont Region of North Carolina, Grade of Membership analysis was applied to all respondents reporting 3 or more somatic symptoms from the somatization disorder section of the Diagnostic Interview Schedule. Seven 'pure' types, roughly analogous to clusters in cluster analysis emerged from the analysis. One 'pure' type in the analysis is nearly identical to DSM-III somatization disorder and is associated with demographic characteristics found among patients with DSM-III somatization disorder. The results indicate that symptoms associated with somatization disorder cluster in a highly predictable fashion and represent a strong validation of the natural occurrence of an entity resembling somatization disorder.