Reliability, validity and minimal detectable change of the Chinese Version of the Assessment of Physical Activity in Frail Older People (APAFOP-C)

Abstract Background Physical activity (PA) is essential in mitigating frailty syndrome, and it is necessary to measure PA in older adults with frailty. Assessment of Physical Activity in Frail Older People (APAFOP) is a suitable patient-reported outcome measure (PROM) for assessing PA among older adults with frailty. This study aimed to determine the reliability, validity and minimal detectable change of the Chinese version of the APAFOP (APAFOP-C). Methods This cross-sectional validation study was designed to measure the reliability and criterion validity of the APAFOP-C with 124 frail community-residing older adults. APAFOP-C was completed twice within an interval of 7–17 days to determine test-retest reliability. The investigator triangulation method was used to investigate inter-rater reliability, and a pedometer was used as the reference measurement to assess the criterion validity. Reliability and criterion validity were assessed using the intraclass correlation coefficient (ICC2,1), Pearson correlation coefficient for normally distributed variables, Spearman correlation coefficient, Wilcoxon signed-rank test for skewed variables, and the minimal detectable change at 95% level of confidence (MDC95). Agreement assessment was conducted using Bland-Altman plots for inter-rater reliability and criterion validity. Kendall’s W test assessed absolute agreement among three raters in inter-rater reliability. The Mann-Whitney U test was used to evaluate whether any particular day was more representative of certain daily activities. Results Total PA on any arbitrarily chosen day illustrates daily activity (Z= -0.84, p = 0.40). The APAFOP-C exhibited strong-to-very strong test-retest reliability (ICC2,1=0.73–0.97; Spearman ρ = 0.67–0.89), and the total PA score demonstrated MDC95