Evaluation Designs Evaluation research has taken two, not indistinct, paths in addressing the complexities inherent in the research situation. First, and most commonly known, evaluators use methods to further 'control' the research situation. A counterfactual is a question that asks what would have happened in the absence of the program initiative. Once the counterfactual is established, the evaluator attempts to control the research setting to answer the question. Controls are required to isolate the influence of program components and remove other variables thought to influence the results.
Evaluators use two main types of controls.
The advantage of random assignment is that with even a moderate number of participants, the chances, statistically, are great the groups will have similar characteristics. In researcher terms, this means that the evaluation does not suffer from selection bias. When comparisons are made between the control and treatment groups, researchers and audiences can conclude that the difference is due to the program and not other variables. Any enthusiasm for random assignment must be weighed against the difficulty in designing research according to this standard. On one hand, there are always ethical issues in determining who gets the treatment and who is made a control.