Design of trials included in the meta-analysis.

*Median year follow-up. PHS = Physicians Health Study. BDT = British Doctor's Trial. TPT = Thrombosis Prevention Trial. HOT = Hypertension Optimal Treatment trial. PPP = Primary Prevention Project.WHS = Women's Health Study. POPADAD = Prevention of Progression of Arterial Disease and Diabetes trial. JPAD = Japanese primary Prevention of Atherosclerosis with Aspirin for Diabetes trial. AAA = Aspirin for Asymptomatic Atherosclerosis trial. ETDRS = the Early Treatment Diabetic Retinopathy Study. APLASA = Antiphospholipid Antibody Acetyl-salicylic Acid study. ECLAP = European Collaboration on Low-Dose Aspirin in Polycythemia Vera study. CLIPS = Critical Leg Ischaemia Prevention Study. ACBS = Asymptomatic Cervical Bruit Study. MCEs = major cardiovascular events; MI = myocardial infarction. Design of trials included in the meta-analysis.