Applying a quantitative bias analysis to estimate attenuation of association between self-reported physical activity and colorectal cancer risk due to measurement error
ISPAH ePoster Library. Lynch B. Oct 15, 2018; 225193; 101
Assoc. Prof. Brigid Lynch
Assoc. Prof. Brigid Lynch
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Abstract Background Although it is well known that self-reported physical activity is inaccurate, few investigators have attempted to adjust for measurement error when computing relative risks for health outcomes. We performed a calibration study and applied the attenuation factor to hazard ratios for physical activity and colorectal cancer risk from a cohort study.MethodsA cohort of 235 Australian adults completed a telephone-administered IPAQ-short, and wore an accelerometer for seven days (Actigraph GTX3+, Freedson cutpoints applied). A validity coefficient and an attenuation factor were calculated from a structural equation model adjusted for age, sex, education and body mass index. The attenuation factor was applied to data from the Melbourne Collaborative Cohort Study to compute bias-adjusted hazard ratios and 95% confidence intervals (CI). ResultsAverage daily minutes of physical activity reported in the IPAQ-short were significantly higher than the duration from accelerometry (54.5 vs 31.7 minutes, p=0.003). The validity coefficient (0.32; 95% CI: 0.20-0.43) and attenuation factor (0.20; 95% CI: 0.12-0.28) were low, indicating substantial measurement error in the IPAQ-short. For participants reporting 150 minutes per week vs no physical activity, the hazard ratio for colorectal cancer risk before and after bias adjustment was 0.88 (95% CI: 0.68-1.13) and 0.52 (95% CI: 0.14-1.94), respectively.Conclusions Over-estimation of physical activity by the IPAQ-short attenuated the association substantially, suggesting that the protective effect of physical activity has been previously under-estimated. Our attenuation factor may provide other researchers using IPAQ-short the opportunity to undertake a quantitative bias analyses within their own studies and adjust estimates.
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