The psychometric properties of the Self-Evaluation of Negative Symptoms Scale (SNS) in treatment-resistant schizophrenia (TRS)

Abstract

BackgroundClinician-administered measures of negative symptoms may not capture patients' subjective experiences. The Self-Evaluation of Negative Symptoms (SNS) has shown good psychometric properties when used in outpatients with higher-level functioning schizophrenia. We aimed to evaluate the psychometric properties of the SNS in low functioning participants with treatment-resistant schizophrenia (TRS). MethodsParticipants were assessed using the following measures at two time-points; time-point 1: SNS, Wide Range Achievement Test, 4th Edition Reading Subtest (WRAT-4), and Brief Assessment of Cognition in Schizophrenia (BACS). Time-point 2 (within a week of time-point 1): SNS, Negative Symptom Assessment 16 items (NSA-16), Scale to Assess Unawareness in Mental Disorder-Abbreviated (SUMD-A), Clinical Global Impression Severity Scale (CGI-S), Simpson Angus Scale (SAS), Calgary Depression Scale for Schizophrenia (CDSS), and the Patient Feasibility Questionnaire. ResultsFifty participants with TRS were enrolled, a mean age of 43.8 years (SD = 11.19, min = 25, max = 64), a mean IQ of 80.62 (SD = 17.12, min = 65, max = 110), and a mean BACS Composite T-Score of 14.08 (SD = 17.16, min = −27, max = 49). Participants responded to SNS prompts with moderate consistency across two time-points. There were no significant correlations between the SNS and the NSA-16 Global Symptom score (Pearson r = 0.207, p = .150, Spearman r = 0.101, p = .483), NSA-16 Global Functioning score (Pearson r = 0.209, p = .145, Spearman r = 0.126, p = .384), nor the NSA-16 total score (Pearson r = 0.149, p = .302, Spearman r = 0.116, p = .421). However, when participants were stratified by BACS Composite T-score, there was a significant positive correlation between the SNS total and the NSA-16 Global Functioning score (Pearson r = 0.500, p = .048, Spearman r = 0.546, p = .029) among participants who demonstrated higher cognitive functioning. ConclusionParticipants with TRS and low functioning were able to respond to questions on the SNS regarding their subjective assessment of negative symptoms. However, self-reported and clinician-rated negative symptoms were not equivalent, except in a subgroup with higher cognitive functioning. This discrepant self-reporting appeared to relate to their low levels of insight and cognitive impairments.