Logic Models and Program Evaluation

Logic models are typically graphical representations of underlying program theory. The U.S. Centers for Disease Control and Prevention (CDC) defines a program logic model as a systematic and visual way to present the perceived relationships among the resources individuals have to operate the program, the activities they plan to carry out, and the changes or results they hope to achieve.

Logic models are used by program managers and evaluators to describe the underlying theory of and the resources and activities required for a program to operate and lead to the desired outcomes and changes. Logic models assist program managers in outlining the resources and activities they need to engage in during program implementation, as well as helping them identify strategies that can be devised for program improvement. Logic models also provide a foundation for evaluating various facets of a program.

For example, an outcome evaluation seeks to assess a program's effectiveness in achieving its goals and objectives. A logic model supports outcome evaluation by providing a comprehensive framework to describe the causal relationships among program components and expected outcomes due to program implementation, thereby facilitating development of evaluation measures. Process evaluation can provide insights about implementation fidelity and, through performance monitoring and continuous quality improvement, these insights can be used by a program manager to revise program implementation. A logic model supports process evaluation by depicting what outcomes can reasonably be expected at a given stage of a program's development.

While there are multiple ways that logic models can be depicted, all logic models describe the “if-then” relationships among program components and the pathways to expected outcomes. Logic models generally have four components: inputs, activities, outputs, and outcomes. Inputs are the human, financial, organizational, and community resources that go into the program, such as staff, money, training, and equipment. Activities are what the program does with these resources. Examples may include training, development of communication and marketing plans, and communication materials or interventions. Outputs are the direct consequences of the program activities (e.g., the people who were trained or received a given intervention). Outcomes are the changes in the target audience or program participants' knowledge, beliefs, attitudes, intentions, or behaviors.

Typically, logic models distinguish between short-term outcomes (attainable within one to three years), intermediate outcomes (within three to five years), or longer-term outcomes (attainable within five or more years). Inputs, activities, and outputs are in the “sphere of influence” of the program manager; in other words, the program [Page 780]manager has direct control over these items and can make adjustments to them accordingly. Outcomes, on the other hand, are results in someone or something other than the program and thus fall outside the manager's sphere of influence.

Because logic models depict a logical and temporal sequence among program components, they illustrate assumptions being made about the causal chain of relationships between these components and the desired outcomes. By doing so, logic models are an expression of a program's “theory,” that is, how a specific program or intervention operates to bring about the desired results. Logic models can also be an expression of the underlying behavioral theory(ies) upon which the program is based, the use of which strengthens the program's likelihood of success in leading to longer-term outcomes. The best logic models provide strong program descriptions (balancing accuracy, thoroughness, and concision) that provide program managers and evaluators with a tool to develop program action and evaluation plans, monitor program performance, adjust the program to ensure the intended outcomes are achieved, and measure the correct outcomes at the right points in time to demonstrate program effectiveness.

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