Case-control studies: Increasing scientific rigor in control selection

The case-control design is an observational study design in which the investigative team identifies individuals with disease (ie, cases) and individuals without disease (ie, controls) and then compares the prevalence of an exposure between the 2 groups. Forethought is needed while designing case-control studies. This is particularly true when selecting controls. This tutorial briefly reviews the case-control design, discusses scenarios of poor case-control study design with an emphasis on control selection, and provides tips for proper control selection. Optimizing control selection to maximize causal inference will increase the scientific rigor of hematologic case-control studies.