A comparison of methods in estimating population attributable risk for colorectal cancer in the United States.

Population attributable risk (PAR) is becoming more widely used for quantifying preventability of cancer. However, its estimations have had a wide range, leading to questions about the true preventability. Our study aimed to compare the two PAR estimation methods (ie, literature-based method and low-risk method) for colorectal cancer (CRC) in the US population based on the same set of modifiable risk factors: physical activity, body mass index, alcoholic drinks, red meat, processed meat, dietary fiber, dietary calcium and cigarette smoking. For the literature-based method, 65% and 53%, and for the low-risk method, 62% and 49% of CRC cases for males and females, respectively, were attributable to the eight dietary and lifestyle risk factors. Additional sensitivity analyses were conducted with respect to the different choices of risk factors, relative risks (RRs) and exposure prevalence estimates used in the literature-based method. The PARs including only the "convincing" factors and excluding "probable" factors defined by the WCRF/AICR were 50% for males and 34% for females. Using RRs derived from different studies changed the PARs considerably (57%-74% for males and 37%-60% for females). Our study assessed the robustness of PAR calculations through a direct comparison between the two methods using different assumptions and data and generally found high concordance. From the additional analyses, we found that the choice of risk factors and RRs could substantially influence the PAR estimates. Given the findings, future studies reporting PAR should consider presenting a range of PAR estimates based on choices of risk factors and RRs.