Sometimes called a “comparison group”, this group does not receive the intervention being evaluated and allows the evaluator to estimate what would have happened if the treatment group had not received the intervention. The control group should be as similar to the treatment group as possible before the intervention is applied. This can be achieved through random assignment or, if randomisation is not possible, matching. There are several types of control group:
Where possible, EEF’s evaluators ensure that a permanent control group is in place so that the long-term impact of an intervention can be estimated.