Dimensional structure and diagnostic specificity of the Frankfurt Complaint Questionnaire.

The Frankfurt Complaint Questionnaire (FCQ) is a widely used method to investigate non-psychotic subjective experiences of schizophrenics. Less is known about its dimensional structure. Therefore, principal components analyses (PCA) were conducted with the FCQ data of 505 schizophrenics and 187 alcoholics. Furthermore, results of a former analysis using item-to-item comparisons between schizophrenics and alcoholics were examined. PCA yielded two factors called 'dysphoric concomitants of severe illness particularly impairing concentration' and 'subjective experiences of perceptual uncertainties'. Neither of the factors was specific to schizophrenia. The item comparisons suggest that only a group of eight FCQ items (subscale 'FCQ-S') is specific to schizophrenia while ten items ('FCQ-A') are related more to alcoholism. The validity of FCQ-S and FCQ-A was confirmed: schizophrenics reached high scores in FCQ-S and low scores in FCQ-A; alcoholics scored high in FCQ-A and low in FCQ-S; schizophrenics with an additional alcohol disorder scored high in both of the subscales. It is concluded that direct group comparisons seem to be promising for the identification of non-psychotic subjective phenomena which are characteristic for schizophrenia.