Test-Retest Reliability and Practice Effect of the Oral-format Symbol Digit Modalities Test in Patients with Stroke

The Symbol Digit Modalities Test (SDMT) is commonly used to evaluate an individual's switching attention and processing speed. However, its test-retest reliability and practice effect are not well known in patients with stroke, limiting its utility in both clinical and research settings. The present study examined the two aforementioned psychometric properties of the oral-format SDMT on a group of 30 outpatients with stroke. The oral-format SDMT demonstrated excellent test-retest reliability (ICC = 0.89) and a small practice effect (Cohen's d = 0.26) within a 1-week interval. A practice effect-corrected reliable change index [-5.29, 10.89] was also provided to help clinicians and researchers interpret their clients' test results. Patients' characteristics and the test-retest interval should be considered before applying the findings of the present study to clinical settings.