Why contamination is a potential problem in program evaluation?

Welcome.

Wonderful. Such a big help!

Contamination is a potential problem in program evaluation because it can compromise the validity of the findings and distort the assessment of the program's true impact. Here are some reasons why contamination is a concern:
1. Lack of isolation: In some program evaluations, it is challenging to completely isolate the treatment group from the control group or individuals who are not part of the program. This lack of isolation creates opportunities for interactions, information sharing, or exposure to the intervention between groups, leading to contamination.
2. Spillover effects: Contamination can occur when individuals or groups in the control group are indirectly affected by the program through spillover effects. This can happen if participants in the treatment group share information, resources, or behavior changes with individuals in the control group, blurring the distinction between the groups.
3. Cross-contamination: In evaluations involving multiple sites or groups, cross-contamination can occur when the intervention effects from one group influence or contaminate the outcomes of another group. This can happen through communication, shared resources, or unintended interactions between the groups.