Figure 4 . Random-effects risk ratio forest plot comparing
any aspirin vs placebo by subgroups. A) Any
adenoma. B) Advanced lesion. Subgroup-specifi c risk
ratios are shown as black squares , with the size of the
square being inversely proportional to the subgroupspecifi
c risk ratio variance. Horizontal lines represent
95% confi dence intervals for the subgroup-specifi c
risk ratios. Overall pooled risk ratios are shown as
diamonds . The middle of each diamond corresponds
to the risk ratio, and the width of each diamond represents
the 95% confi dence interval. The vertical
dashed line provides a visual comparison of the
pooled risk ratio with the subgroup-specifi c risk
ratios. P values (two-sided) are based on Wald tests
for interaction. Among those with follow-up data,
body mass index was missing for 173 participants in
the aspirin groups and 142 participants in the placebo
group; family history of colorectal cancer was
missing for 532 participants in the aspirin groups and
451 participants in the placebo group, including all
participants in Cancer and Leukemia Group B (CALGB
9270); number of lifetime adenomas at baseline was
missing for 261 participants in the aspirin groups and
260 participants in the placebo group, including all
participants in CALGB 9270; advanced-lesion status
at baseline was missing for 96 participants in the
aspirin groups and 71 participants in the placebo
group, with participants in CALGB 9270 being
excluded from this subgroup analysis. CI = confi -
dence interval.