BetterEvaluation FAQ: How do I choose a suitable theory of change?

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A theory of change can be very useful in designing an impact evaluation, but what kinds of theories should we use?

We've been getting some great questions recently - so we're starting to share our answers through these blogs.  We'd welcome any additional suggestions for how to respond, or useful resources.

I want to do an impact evaluation. What kinds of theories should I use for developing a theory of change?

A theory of change can be very useful in designing an impact evaluation.  It can identify what you should collect data about and how help guide how it should be analysed and reported.  

It's important to make sure that the theory of change actually has a theory about how change will come about  - not just some boxes with arrows between activities and outcomes/impacts.

So how do you choose which change theory to use? There are a number of options and in practice it's often useful to combine these:

1. Identify the "big t" Theories from previous research and evaluations

Previous research in the relevant area often discusses how change occurs at different levels - for individuals, families, communities and organisations. Reviewing this research can help to identify possible "big t" Theories, and give you an understanding of which might be most appropriate. 

For example, in relation to theories for behaviour change, a systematic review undertaken by Susan Michie et al. (2011) identified  83 different behaviour change theories!  

You might find one of these particularly relevant. or their summary overview which has three clusters: capabilities (skills and knowledge), motivation (positive and negative, intrinsic and extrinsic) and opportunities.


The COM-B system - A Framework for Understanding Behaviour. Michie et al. Implementation Science, 2011, 6:42

There might also be middle-range theories such as deterrence that have relevance. 

Sometimes there are specific change theories related to the sector.  For example if you wanted to evaluate the impact of a purchase of a defence procurement project, a review of research in the area search on Defence Policy theory might come up with a few leads.  The Common Security and Defence Policy and IR Theory gives a short overview of a few relevant theories (e.g. Liberal Institutionalism, Materialism, and realism), and a paper on Realism and the Common Security and Defence Policy also has some options.

A systematic review would identify more theories, and give you an understanding of which "big t” Theories might be most appropriate in your particular case.

2. Look at the theories implicit in the policy documentation, including any background papers.

It’s always a good idea to go back to the project’s documentation, especially any background papers on the policy. It's particularly important to identify any theories which have been explicitly referred to in discussions or decisions.

For example, some crime prevention programs make explicit reference to  the "broken window" theory of crime prevention  - which is that signs of disorder such as unrepaired broken windows leads to increased withdrawal by local residents, and decreased informal social control, creating more opportunity for serious crime to move in. (The Center for Evidence-Based Crime Policy has more information on the theory and the evidence about whether and when it holds). 

3. Draw out the mental models of those involved. 

Articulating mental models involves talking individually or in groups with key informants (including program planners, service implementors and clients) about how they understand an intervention works. If you can't talk with them, you might be able to find notes from discussions about how the program or project is meant to work.

Our Method page on Articulating Mental Models has a list of questions that can be used to draw out these mental models.

4. Logical analysis of the causal paths - how might the dots be connected?

In addition to these sources, it can be useful to logically analyse the actors and possible causal paths.  For example, in a program involving home visits by teachers, improvements to student learning might come about through changes in the teachers (for example, learning about barriers to students' learning such as lack of study spaces at home), the students (for example, developing a better relationship with the teacher), or through the parents (for example, developing a willingness to support school processes).

These different possible theories can be explored in discussions (while exploring existing mental models) and when reviewing research and project documentation.

What are the strategies you use to identify possibly relevant theories for your theory of change?

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