Control Group

A control group is a population, within a study, that is compared with an experimental group. An attempt is made to make the control group as like as possible to the experimental group in all factors except in the factor of interest. A historical control group involves using individuals or data that were collected earlier in time than the experimental group. As risks, prognosis, and management can vary over time, using a historical control group introduces a potential bias into the experiment. To eliminate these potential variables, a case–control study can be used where both the experimental and control groups are chosen at the same time and matched as closely as possible except for the experimental variable. In a case–control study, a person with a disease (a case) is compared with the control population, consisting of people with the same risk factor but without the disease of interest. Bias is introduced, because individual recall of exposure to risks factors plays a significant role. However, this study design is frequently used as a preliminary investigation because data are relatively quick and inexpensive to obtain. In a randomized controlled trial (a type of prospective study), the participants are randomly allocated to either the experimental or the control group. The experimental design introduces the study variable and the data must be analyzed to determine if the two groups differ statistically with regard to nonexperimental variables. In a crossover study, each individual receives each specific treatment and functions as his or her own individual control.