Importance of the baseline risk in determining sample size and power of a randomized controlled trial

Accurate estimation of adequate sample size to reduce the possibility of a type II error (false negative) is important in planning a randomized controlled trial (RCT). It becomes apparent that many recent critical care trials could not reject the null hypothesis; so much so that the proportion of clinical trials rejecting the null hypothesis on crude mortality outcome was close to the conventional acceptable type I error (5%) (1).