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Reliability of a measure of prediagnosis physical activity for cancer survivors
Brigid M Lynch1, Neville Owen, Beth Newman
1Viertel Centre for Research in Cancer Control, Queensland Cancer Fund, Brisbane, Australia. blynch@qldcancer.com.au
Purpose:
This study was conducted to examine the test-retest reliability of a measure of prediagnosis physical activity participation administered to colorectal cancer survivors recruited from a population-based state cancer registry.
Methods:
A total of 112 participants completed two telephone interviews, 1 month apart, reporting usual weekly physical activity in the year before their cancer diagnosis. Intraclass correlation coefficients (ICC) and standard error of measurement (SEM) were used to describe the test-retest reliability of the measure across the sample; the Bland-Altman approach was used to describe reliability at the individual level. The test-retest reliability for categorized total physical activity (active, insufficiently active, sedentary) was assessed using the kappa statistic.
Results:
When the complete sample was considered, the ICC ranged from 0.40 (95% CI: 0.24, 0.55) for vigorous gardening to 0.77 (95% CI: 0.68, 0.84) for moderate physical activity. The SEM, however, were large, indicating high measurement error. The Bland-Altman plots indicated that the reproducibility of data decreases as the amount of physical activity reported each week increases. The kappa coefficient for the categorized data was 0.62 (95% CI: 0.48, 0.76).
Conclusion:
Overall, the results indicated low levels of repeatability for this measure of historical physical activity. Categorizing participants as active, insufficiently active, or sedentary provides a higher level of test-retest reliability.
