Road Safety Project Plan - Logic Model

Why and How an intervention should achieve its aims

One of the first jobs to do in an evaluation is to look at the model of why and how the intervention is expected to achieve the anticipated result. This is the theory of change behind the intervention being evaluated and is simply the intervention planners' understanding of exactly why it should 'work'.

A logic model is a technical term for a certain type of project plan. It is usually put onto a single piece of paper. Developing a logic model helps others to understand how the intervention is expected to achieve what it plans to achieve. Ideally, the model is developed at the design stage of the project but one can be created at any point.

In its simplest form, a logic model breaks the intervention down into inputs, outputs and outcomes. It is essentially a trail of how the resources (the inputs) and the delivered activities/services (the outputs) lead to the intended change (the outcomes). It is a chain of events:

  Inputs Outputs Outcomes
Example 2 Staff 12 Presentations delivered Change in knowledge and attitude

Using the logic model an evaluator can see what to measure. For instance, were there any problems with delivery of the workshops? Was there an increase in knowledge from before the intervention?

There are two further elements to the logic model that you should also include. The first is external factors. These are factors that are outside your control but may still affect the success of the intervention. For example, another body may be delivering similar presentations in the same region.

The second element is the 'intervention assumptions'. These assumptions are the beliefs about how the intervention outputs will cause the intended outcomes.

Using the above example, the assumption might be that the presentation audience will engage with the content and with the presenters; relate to what they hear; challenge their own previous beliefs; and remember what they learned.

Logic models are often depicted in the form of a sequential table or a flow-chart diagram. See for the logic model for E-valu-it.

For more information, see our Workshop Materials page for an exercise on building logic models.


  1. Hills, D. (2010) Logic mapping: hints and tips for better transport evaluations. Travistock Institute
  2. Clarke, A. (2000) Evaluation Research: An Introduction to Principles, Methods and Practice London: Sage
  3. McDavid, J. C. and Hawthorn, L. R. L. (2006) Program Evaluation and Performance Measurement: An Introduction to Practice London: Sage.
  4. Millar, A., R.S. Simeone, and J.T. Carnevale. 2001. ‘Logic models: a systems tool for performance management'. Evaluation and Program Planning 24:73-81.