<qa>  What is the efficacy of clopidogrel?- To assess the efficacy of clopidogrel 75 mg once-daily by comparison with a placebo, in preventing cardiovascular morbiditymortality. The study will compare the efficacy of the two regimens in preventing the occurrence of major cardiovascular complications stroke, heart attack, cardiovascular death in high-risk patients who are otherwise receiving low-dose aspirin therapy 75-162 mg daily. 