Validity of symptom assessment in psychotic disorders: information variance across different sources of history.
BACKGROUND: Factors such as poor insight, amotivation, suspiciousness, disorganized speech and attentional problems may interfere with the ability of acutely ill individuals with psychotic disorders to provide a valid account of their symptoms. This study was designed to determine the degree to which history provided by such subjects is consistent with that obtained from other sources. METHOD: Fifty-five subjects presenting with psychotic disorders were multiply evaluated with a semi structured interview, the Comprehensive Assessment of Symptoms and History (CASH), which includes the Scales for the Assessment of Negative and Positive symptoms (SANS and SAPS). One interviewer assessed the severity of the patient's symptoms in the previous month based solely on information provided by the patient. A second rater made symptom ratings based on information obtained from a "best informant". Following this, a consensus rating was established based on an extensive evaluation and review of all sources of information. An item-by-item comparison of the three sets of symptom ratings was then quantified by paired t-tests, simple and multiple correlations. RESULTS: Positive and negative symptoms ratings based on the subjects' report were significantly lower than the corresponding consensus ratings. However, those based on the informants' report did not differ from consensus ratings for negative symptoms. Information obtained from subjects and from informants together accounted for a majority of the variance of the consensus ratings. CONCLUSIONS: These findings demonstrate that assessment limited to patients' own reports are likely to underestimate psychopathology in acutely ill patients with psychotic disorders. Obtaining corroborative history from a family member may substantially improve the validity of the assessment of negative symptoms.