Abstract

The reuse of subjects in clinical studies to answer specific research questions is a common practice. This reuse can take many forms and is at least partly related to study efficiency. It is much easier to reuse known subjects who know the system(s) or are easy to find than to recruit new ones. A hypothetical question is: Are there instances when such practices may not be scientifically valid? This question will be addressed from the perspective of the case‐control and experimental study design.