2.2. Study Selection

Literature eligibility was assessed by two investigators independently; discordant conclusions were resolved through discussion and consensus. Inclusion criteria were as follows: (1) the study was a cohort study or case-control study because of higher quality of evidence-based medical evidence; (2) reviews, case reports, letters, comments, and lectures were excluded; (3) the authors reported data from an original, peer-reviewed study; and (4) the exposure interest was aspirin exposure and the outcome was death, and the investigators reported multivariate-adjusted risk estimates with 95% confidence intervals (CIs). When articles had the same data source or included multiple publications, the articles of the most informative one or with the higher quality were included.