Questioning Medicine

 What is the power of a study—what is the power calculation? Often say it is the number of people in a study. Power is the probably to correctly reject the null hypothesis. Said differently power is the probability we will correctly get a small pvalue But a power calculation is slightly more than that it is the number of people required to adequetyly statistically calculate the number of people that would be necessary to reject your null hypothesis of no difference when there actually is a difference. Lets say we have a blood pressure drug and we want to see if it works Well if you only enroll a small number of people you might not be able to tell a difference between those in the active and those in the control arm Remember depending on baseline bp you might only see a 4-5mmg hg improvement in your blood pressure and in almost every trial I have ever seen even those individuals that get the placebo have a 1-2mm hg improvement in their bp so with large confidence intervals that are likely to overlap with just