We combined data from all randomized double-blind placebo-controlled trials that evaluated aspirin for
the prevention of colorectal adenomas. We used random-effects meta-analysis to estimate risk ratios and
95% confidence intervals (CIs) for the effect of aspirin on the occurrence of adenomas and of advanced
lesions (ie, tubulovillous adenomas, villous adenomas, adenomas ≥ 1 cm in diameter, adenomas with
high-grade dysplasia, or invasive cancer). All statistical tests were two-sided.