Internal Validity

Internal validity refers to the evidence that the interpretations and conclusions reached in the evaluation can be attributed to program functions rather than to other factors. Poorly designed outcome evaluations, by definition, have questionable integrity because of insufficient safeguards against alternative explanations for program effects; program outcome effects are intractably enmeshed with extraneous factors. The design challenges for evaluation studies are similar to those in traditional research in that a system of logic must be applied that enables the designer to construct procedures that will reduce the irrelevant sources of program outcome variability before the evaluation is conducted.

For example, gathering evidence of program fidelity, that is, evidence that the program features that are the object of the evaluation were actually implemented, should be part of ...