Besides these heterogeneities, several limitations in the methods of included studies require comment. In most of the studies,15,17,22- 25,28- 30 outcomes were not adjudicated in a blinded fashion for laboratory aspirin resistance, making them more susceptible to bias. In 1 study,24 45 patients were excluded for reasons that were not mentioned, and in another study,25 allocation to either aspirin or clopidogrel was not randomized but was based on patients' concerns. Moreover, use of nonsteroidal anti-inflammatory drugs, which may have differed among studies because it was not a formal exclusion criterion in 9 of them,15- 18,21,25- 27,29,30 could have influenced the prevalence of laboratory aspirin resistance.31- 33 Furthermore, laboratory aspirin resistance was only determined on a single occasion in all but 4 studies,23,24,27,29 which may have led to misclassification of patients. For example, persistent platelet reactivity may be more common after coronary artery bypass grafting owing to increased platelet turnover.34 This temporal “resistance” was recently observed in a population of patients who had undergone coronary bypass.27 Although noncompliance with treatment is an important cause of laboratory aspirin resistance,21,35 patient adherence to treatment was assessed in only 3 studies.16,21,24 Cotter et al21 have suggested that after exclusion of noncompliant patients, laboratory aspirin resistance is no longer related to recurrent events.