GAO-12-208G, Designing Evaluations: 2012 Revision

Net Impact Evaluations
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Chapter 2: Defining the Evaluation’s Scope
longer-term outcomes. For example, it might take a study 3 or more years
to observe whether a program for high school students led to greater
success in college.
Where a program’s desired outcomes are known to also be influenced
appreciably by factors outside the program, such as the labor market, the
outcomes that are actually observed represent a combination of program
effects and the effects of those external factors. In this case, questions
about program effectiveness become more sophisticated and the
evaluation design should attempt to identify the extent to which the
program caused or contributed to those observed changes. Impact
evaluation is a form of outcome evaluation that assesses the net effect of
a program (or its true effectiveness) by comparing the observed
outcomes to an estimate of what would have happened in the absence of
the program. While outcome measures can be incorporated into ongoing
performance monitoring systems, evaluation studies are usually required
to assess program net impacts.
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GAO. 2000. Managing for Results: Views on Ensuring the Usefulness of
Agency Performance Information to Congress, GAO/GGD-00-35.
Washington, D.C.: Jan. 26.
GAO. 2002. Program Evaluation: Strategies for Assessing How
Information Dissemination Contributes to Agency Goals, GAO-02-923.
Washington, D.C. Sept. 30.
Bernholz, Eric, and others. 2006. Evaluation Dialogue Between OMB
Staff and Federal Evaluators: Digging a Bit Deeper into Evaluation
Science. Washington, D.C.: July.
http://www.fedeval.net/docs/omb2006briefing.pdf
Rossi, Peter H., Mark W. Lipsey, and Howard E. Freeman. 2004.
Evaluation: A Systematic Approach, 7th ed. Thousand Oaks, Calif.: Sage.
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