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.