Practice Effects and Test-Retest Reliability of the Continuous Performance Test, Identical Pairs Version in Patients with Schizophrenia over Four Serial Assessments

OBJECTIVE: The purposes of this study were to examine the practice effects and test-retest reliability of the Continuous Performance Test, Identical Pairs version (CPT-IP) over four serial assessments in patients with schizophrenia. METHOD: Fifty-six patients with schizophrenia were assessed with the CPT-IP four times, once per week. The CPT-IP contains four indices: "2-digit score," "3-digit score," "4-digit score," and "total score." RESULTS: The four indices showed trivial-to-small practice effects (Cohen's d = -0.13-0.24), good-to-excellent test-retest reliability (ICC = 0.62-0.88), and unacceptable random measurement error (MDC% = 33.8%-110.8%). CONCLUSIONS: The total score had the best reliability among the four indices. Although practice effects of the four indices all appeared cumulative, all four CPT-IP indices reached a plateau after the second assessment. These results indicate that clinicians should interpret the change scores of the CPT-IP conservatively and use the total-score index in their routine repeated assessments.