[A necessary number or subjects... to conclude].
The fact that a difference is not statistically significant does not mean that it does not exist. Some differences are not demonstrated by studies conducted on small sample sizes due to random sampling fluctuations. To demonstrate a difference which really exists or to conclude on the absence of a difference, the study must have a sufficient power, essentially determined by the number of subjects included. In the case of comparisons of survival curves, the number of events or total deaths at the time of analysis determines the power of the study. Examples derived from the urological or theoretical literature will illustrate the value of calculating the number of subjects required before starting the study and the value of retrospectively evaluating the power of a study in order to interpret its results.
Glemain
P
P
Clinique Urologique, Hôtel Dieu, Nantes, France. pglemain@chu-nantes.fr
D002986:Clinical Trials as Topic / Q000592:standards*; D006801:Humans; D018401:Sample Size