Test-retest reliability of the Wisconsin Card Sorting Test in people with schizophrenia

Purpose: The aim of this study was to examine the test-retest reliability of the Wisconsin Card Sorting Test in people with schizophrenia. In this study, minimal detectable change (MDC) was calculated and systematic measurement errors were evaluated. Method: Sixty-three people with schizophrenia underwent the WCST twice with a two-week interval. Test-retest reliability was evaluated using intraclass correlation coefficient. Systematic measurement error was examined using paired t-test and effect size (Cohen's d). Results: The values of intraclass correlation coefficient were >0.70, except for two indices ("nonperseverative errors" and "failure to maintain set" with intraclass correlation coefficient of 0.56 and 0.30, respectively). Seven indices showed nonsignificant differences between the two assessments (t(62)= -0.84 to 1.38, p > 0.05) and negligible effect sizes (d = 0.03-0.13). The values of MDC with 95% certainty were 32.3, 42.0, 31.2, 36.9, 40.1, 3.3, and 3.8 for the "total number correct," "perseverative responses," "perseverative errors," "nonperseverative errors," "conceptual level responses," "number of categories completed," and "failure to maintain set" indices, respectively. Conclusions: The WCST has acceptable test-retest reliability. Two indices ("nonperseverative errors" and "failure to maintain set") revealed lower levels of consistency in scores over repeated assessments. Clinicians and researchers should be cautious when using these two indices to interpret of the re-assessment results in people with schizophrenia.