Statistical analysis
The relationship between follow-up and baseline U-TXM was plotted (on a log scale), distinguishing categories by adherence to study aspirin/placebo tablets (reported on the sampling form) and non-study aspirin use. Participants were classified as non-adherent (last tablet date earlier than the day before sampling, or known to be taking non-study aspirin); last tablet taken ≤ 12 h before sample; last tablet taken > 12 h before sample; and adherent but the time of taking tablet not known (distribution of timings shown in Fig. SComparisons by intention-to-treat, and restricting by adherence, were of mean log U-TXM at follow-up by aspirin allocation (without adjustment for baseline values). A preliminary analysis had shown that the Pearson correlation between log U-TXM measurements at baseline and follow-up among adherent participants in the placebo arm was weak (0.48), indicating little improvement would be gained by adjustment for baseline levels (and hence baseline samples were not assayed for the additional adherent sample participants) [