To some, field experiments represent the gold standard in program evaluation. There are a number of different ways to design experiments but at heart they all involve comparisons between those who received a program (sometimes called the treatment group) and those who did not (sometimes called the control group). Sometimes, outcomes are assessed across different groups of people. Other times, participants are assessed prior to their involvement with a program and then again afterwards.
There are a multitude of factors that go into creating valid experiments including such things as whether or not those in the treatment group are similar to those in the control group in every way except participation in the program. Few non-profit programs have the capacity to design and administer a field experiment. While they may be well suited to assessing a program’s outcomes, they often do not provide the kind of information necessary for understanding how those outcomes come about.