This study aimed to examine the reliabilities (test-retest reliability and measurement error), construct validity, and the interpretability (minimal clinically important difference) of the Box and Block Test (BBT) to interpret test scores precisely for children with UCP. A total of 100 children with UCP were recruited and 50 children from the whole sample assessed the BBT twice within 2-week interval. The BBT, the Melbourne Assessment 2, the Bruininks-Oseretsky Test of Motor Proficiency, 2nd Edition, and the Pediatric Motor Activity Log Revised were measured before and immediately after a 36-h intensive neurorehabilitation intervention. Measurement properties of the BBT were performed according to the COnsensus-based Standards for the selection of health Measurement INstruments checklist. The test-retest reliability of the BBT was high (intraclass correlation coefficient = 0.98). The measurement error estimated by the MDC95 value was 5.95. Construct validity was considered good that 4 of 4 (100%) hypotheses were confirmed. The interpretability estimated by the MCID ranged from 5.29 to 6.46. The BBT is a reliable and valid tool for children with UCP. For research and clinical applications, an improvement of seven blocks on the BBT is recommended as an indicator of statistically significant and clinically important change.
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