Читать книгу Interventional Cardiology - Группа авторов - Страница 148

Any estimate of treatment effect in a clinical trial contains some random error, and calculating a confidence interval (CI) enables one to see within what range it is plausible that the true effect lies. For instance, the observed relative risk for 30‐day all cause mortality in the Safety and Efficacy of Femoral Access vs Radial Access in ST‐Segment Elevation Myocardial Infarction (SAFARI‐STEMI) trial is 1.15, while the 95% CI is 0.58–2.30 [2]. This means that one is 95% sure that the true relative risk is in this interval. To be precise, there is a 2.5% chance that the true RR lies below 0.58 and 2.5% that the true RR is greater than 2.30. The larger the sample size, the tighter the CI becomes. Specifically, to halve the CI width one needs a trial four times the size.