The use of well controls: an unhealthy practice in psychiatric research

Background. Studies comparing cases with controls to uncover the causes of psychiatric disorders are common in biological research. The validity of these studies depends upon adherence to the methodological principles underlying the case-control design. However, these principles are often violated. One common practice that violates these principles is the use of well controls. In this paper we describe the bias that it can cause and discuss why the use of well controls leads to invalidity in case-control studies. Method. Using hypothetical numerical examples we illustrate the consequences of using well controls. Results. The results illustrate that the use of well controls can cause substantial bias. In no instance does the use of well controls improve validity. Conclusions. We conclude that the use of well controls is an unhealthy practice in psychiatric research.