In their nested case-control study on aspirin use and mortality in women within the Nurses Health Study, Chan et al1 conclude that aspirin use is associated with a decreased mortality. The reported effect is clearly stronger than results of previous randomized controlled trials suggested. The effect of aspirin in this study may be overestimated for 2 reasons that are remediable.
Snoep JD, Dekkers OM, Vandenbroucke JP. A Possible Overestimation of the Effect of Aspirin. Arch Intern Med. 2007;167(21):2372–2373. doi:10.1001/archinte.167.21.2372-b