Reliability and validity of the Dutch version of the International Physical Activity Questionnaire in patients after total hip arthroplasty or total knee arthroplasty.

STUDY DESIGN Psychometric assessment. OBJECTIVES To determine test-retest reliability and concurrent validity of the International Physical Activity Questionnaire (IPAQ) in patients after total hip arthroplasty or total knee arthroplasty. BACKGROUND Despite recognized benefits of regular physical activity, little is known about the physical activity level of patients after total hip arthroplasty or total knee arthroplasty. None of the currently used questionnaires is internationally accepted. The IPAQ tries to address this problem, but its validity and reliability in those who have had a total hip arthroplasty or total knee arthroplasty are unknown. METHODS Forty-four patients completed the IPAQ (short and long forms) twice. Test-retest reliability was assessed by Spearman correlation coefficients (r) and intraclass correlation coefficients. Additionally, standard error of measurement and minimal detectable change were calculated. Concurrent validity was determined by an accelerometer. Spearman correlation coefficients were calculated between IPAQ scores and accelerometer data. Bland-Altman analyses were performed for both reliability and validity. RESULTS Fair to good correlation coefficients were found for test-retest reliability of the total and activity scores (r = 0.49-0.81, intraclass correlation coefficient = 0.27-0.71). Standard error of measurement and minimal detectable change were large. For concurrent validity, weak to moderate correlation coefficients were found for total and activity scores (r = -0.07 to 0.54). Systematic bias was found between the IPAQ and accelerometer data, with higher scores on the IPAQ. CONCLUSION Overall, the IPAQ showed fair reliability and weak concurrent validity. These results are in line with previous studies of the reliability and validity of the IPAQ. Due to systematic bias and large standard error of measurement and minimal detectable change, the IPAQ may only be suitable for intergroup comparisons.