Measuring the Burden of Schizophrenia Using Clinician and Patient-Reported Measures: An Exploratory Analysis of Construct Validity.

backgroundVarious self-reported or clinician-reported (as a proxy) measures exist to quantify the burden of schizophrenia on patients. Evidence of the psychometric relationship between these measures to inform their practical use is limited.

objectivesOur objective was to conduct an exploratory analysis of the construct validity of patient-reported (EQ-5D, SF-6D, WEMWBS, SQLS subscales of Psychosocial, Motivation, Symptoms) versus clinician-reported measures (PANSS, CGI-SCH, NSA-4, HoNOS-PbR) to inform future use of patient-reported measures for burden-of-illness assessment and/or economic evaluation.

methodsIn an adult patient population with schizophrenia, construct validity was assessed in relation to convergent and known-group validity. Convergent validity was assessed using Spearman's rank absolute correlation strength (ACS: weak ≤ 0.3, moderate = 0.3 < 0.5, strong ≥ 0.5) and graphically using locally weighted scatterplot smoothing (LOWESS) techniques. Known-group validity was assessed using Cohen's d absolute effect size (AES: small ≤ 0.5, moderate = 0.5 < 0.8, large ≥ 0.8). Floor and ceiling effects were assessed as a proxy of sensitivity in this cross-sectional study. Statistical significance was assessed at the 5% threshold level (p < 0.05). Across head-to-head assessments, the frequency of producing the strongest ACS, largest AES, and statistically significant results determined the best overall construct validity.

resultsOverall, 304 patients consented to the study. In relation to statistically significant results, the SF-6D most frequently exhibited the strongest ACS and largest AES against the clinician-reported measure scores (ACS range 0.084-0.436; AES range 0.043-0.746), and the SQLS Motivation subscale most frequently exhibited the weakest/smallest values (ACS range 0.009-0.157; AES range 0.002-0.397), although these results were mixed according to the clinician-reported measure used for comparative analysis (ACS range 0.009-0.529; AES range 0.002-0.934).

conclusionThe SF-6D indicated the best (mostly moderate) construct validity but still missed the negative symptoms of the condition. Although further evidence is required to confirm or refute these exploratory results, compared with the EQ-5D, the SF-6D can be self-reported to better capture generic health-related quality-of-life aspects of schizophrenia for the purpose of economic evaluation. The lack of construct validity for SQLS Motivation and Symptoms subscales were hypothesized post-hoc to be representative of the complementary information elicited by the subscales not captured by the clinician-reported measures. Therefore, the SQLS can be self-reported to capture complementary (i.e., additional) information relative to clinician-reported measures.