Not-so-surprising findings

Not-so-surprising findingsInvestigators who publish their research in medical journals usually report effect measures in the form of ratios, such as relative risk or rate ratio.It is well known that the magnitude of ratio measures depends on the underlying risk for the study outcome: 1 the higher the baseline risk in a population, the lower the risk ratio for a constant excess risk (Fig. 1).Randomized controlled trials (RCTs) often include only low-risk patients, selected through stringent exclusion criteria, wheras epidemiologic studies usually include typical patients with multiple comorbidities.These differences in baseline risk lead to higher ratio effect measures in RCTs than in nonrandomized studies, which would explain some of the observations reported by Panagiotis Papanikolaou and associates. 2 Of relevance to this point is their scenario 15 on the risk of myocardial infarction in the context of therapy with rofecoxib or naproxen. 2Table 1 shows the difference in risk structure and baseline event rates between the VIGOR trial 3 (which focused on gastrointestinal effects and excluded patients with major cardiovascular conditions) and the nonrandomized study by Ray and colleagues. 4These differences resulted in numerically higher rate ratio measures in the RCT (because of the lower baseline event rate), despite smaller rate differences.In meta-analytic comparisons between RCTs and nonrandomized studies that fail to adjust for the re-Letters