Development and validation of IMPACT-S, an ICF-based questionnaire to measure activities and participation

Objective: IMPACT-S is the screener part of the ICF Measure of Participation and ACTivities questionnaire. IMPACT-S consists of 33 items in 9 scales, reflecting the 9 activity and participation chapters of the International Classification of Functioning, Disability and Health (ICF). The reliability and validity of IMPACT-S as an independent brief measure of activities and participation was examined. Design: Repeated administration of a postal questionnaire. Patients: Road accident victims were recruited through several Dutch hospitals and rehabilitation centres. A total of 276 patients participated and 197 took part in both measurements. Methods: Examination of test-retest reliability, reproducibility and construct validity. The World Health Organization Disability Assessment Schedule II (WHODAS-II) was included as criterion measure for concurrent validity. Results: Types of main injury were fractures (38%), traumatic brain injury (37%), spinal cord injury (13%), whiplash (9%) and other (3%). Mean time after injury was 2.2 years. Internal consistency of IMPACT-S was satisfying for all 9 domains (0.75-0.89) and excellent for the total score (0.96). Test-retest reliability was good at item level (0.44-0.72), domain level (0.72-0.92) and total score (0.94). Strong correlations (0.61-0.88) between IMPACT-S and corresponding WHODAS-II scores were found. Conclusion: IMPACT-S is a reliable and valid generic measure of activity limitations and participation restrictions that fits the ICF.