Assessment of trait and state aspects of depression in schizophrenia.

Depression and negative symptoms can be difficult to distinguish in schizophrenia. Assessments for negative symptoms usually account for the longitudinal nature of these symptoms, whereas instruments available to measure depression mainly assess current or recent symptoms. This construct difference may confound comparison of depressive and negative symptoms in schizophrenia because both domains may have trait-like aspects. We developed an instrument to measure both longitudinal "trait" as well as recent "state" symptoms of depression and tested this instrument (Maryland Trait and State Depression [MTSD] scale) in a sample of 98 individuals with schizophrenia or schizoaffective disorder and 115 community participants without psychotic illness. Exploratory factor analysis of the MTSD revealed 2 factors accounting for 73.4% of the variance; these 2 factors corresponded with "trait" and "state" depression inventory items. Neither MTSD-state nor MTSD-trait was correlated with negative symptoms as measured with the Brief Negative Symptom Scale (r = .07 and -.06, respectively) in schizophrenia patients. MTSD state and trait scores were significantly correlated with the Brief Psychiatric Rating Scale depression subscale (r = .58 and .53, respectively) as well as the Profile of Mood States depression subscale (r = .57 and .44). Persons with schizophrenia had significantly greater trait depressive symptoms than controls (P = .031). Individuals with schizoaffective disorder had significantly higher trait depression (P = .001), but not state depression (P = .146), compared with schizophrenia patients. Trait depressive symptoms are prominent in schizophrenia and are distinct from negative symptoms.