Control Groups

Evaluation designs can be broadly classified into three categories: experimental, quasi-experimental and non-experimental. The term control group is used when the evaluation employs an experimental design and the term comparison group is associated with a quasi-experimental design. In non-experimental design, program participants are compared to non-participants by controlling statistically for differences between participants and non-participants. These three evaluation designs vary in feasibility, cost, the degree of clarity and validity of results, and the degree of selection bias. <span />

The comparison/control group should be as similar to the target group as possible, but for the fact that its members do not participate in a program or receive the intervention. An estimate of impact can then be derived by comparing the levels of well-being between comparison/control groups and the target group (those who do receive the intervention).

  

Source:

World Bank –Impact Evaluation (2008): http://web.worldbank.org/WBSITE/EXTERNAL/TOPICS/EXTPOVERTY/EXTISPMA/0,,contentMDK:20188242~menuPK:415130~pagePK:148956~piPK:216618~theSitePK:384329,00.html