A Quantitative Bias Analysis to Estimate Measurement Error-Related Attenuation of the Association Between Self-Reported Physical Activity and Colorectal Cancer Risk

Shahid Mahmood, Nga H. Nguyen, Julie K. Bassett, Robert J. MacInnis, Amalia Karahalios, Neville Owen, Fiona J. Bruinsma, Roger L. Milne, Graham G. Giles, Dallas R. English, Brigid M. Lynch

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Background: Self-reported physical activity is inaccurate, yet few investigators attempt to adjust for measurement error when estimating risks for health outcomes. We estimated what the association between self-reported physical activity and colorectal cancer risk would be if physical activity had been assessed using accelerometry instead. Methods: We conducted a validation study in which 235 Australian adults completed a telephone-administered International Physical Activity Questionnaire (IPAQ), and wore an accelerometer (Actigraph GT3X+) for 7 days. Using accelerometer-assessed physical activity as the criterion measure, we calculated validity coefficients and attenuation factors using a structural equation model adjusted for age, sex, education and body mass index. We then used a regression calibration approach to apply the attenuation factors to data from the Melbourne Collaborative Cohort Study (MCCS) to compute bias-adjusted hazard ratios (HR) and 95% confidence intervals (CI). Results: Average daily minutes of physical activity from the short form of the International Physical Activity Questionnaire (IPAQ-short) were substantially higher than accelerometer-measured duration (55 versus 32 min). The validity coefficient (0.32; 95% CI: 0.20, 0.43) and attenuation factor (0.20; 95% CI: 0.12, 0.28) were low. The HRs for colorectal cancer risk for high (75th percentile; 411 min/week) versus low (25th percentile; 62 min/week) levels of self-reported physical activity were 0.95 (95% CI: 0.87, 1.05) before and 0.78 (95% CI: 0.47, 1.28) after bias adjustment. Conclusions: Over-estimation of physical activity by the IPAQ-short substantially attenuates the association between physical activity and colorectal cancer risk, suggesting that the protective effect of physical activity has been previously underestimated.
Original languageEnglish
Pages (from-to)153-161
Number of pages9
JournalInternational Journal of Epidemiology
Issue number1
Publication statusPublished - Feb 2020


  • Measurement error
  • self-reported physical activity
  • calibration
  • attenuation factor
  • validity coefficient
  • accelerometry
  • bias-adjusted hazard ratio
  • IPAQ
  • structural equation model
  • quantitative bias

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