We present the results as odds ratios with 95% confidence intervals. We considered a two tailed P value of less than 0.05 as significant. Calculations were done using the fixed effects model. Heterogeneity was assessed using the Q test (a search being initiated by a heterogeneity >50%). Finally, we determined the robustness of our findings by removing the most positive studies one at a time. Planned sensitivity analyses were assessment of the platelet function assays, dose of aspirin, and the inclusion of another platelet inhibitor. We used a computer assisted S-plus/R function to fit meta-analytic mixed random and fixed effects models to do a metaregression analysis of any dose response.19 Potential publication bias was assessed by a funnel plot, and we used an Egger’s regression test to assess any dose related effect.20 We used the checklist recommended by the meta-analysis of observational studies in epidemiology group.21