» Theory of Change (ToC) and Diagrammatic Logic Models
The theory of change explains how an intervention is intended to produce the desired effect. It entails making hypothesis about the causal mechanisms by which the components and activities of an intervention will lead to outcomes. The logic model is a diagrammatic presentation of the theory of change.
The UK Medical Research Council’s (MRC) guidance to the development and evaluation of complex intervention notes that identifying and developing a theoretical understanding of the likely process of change is a key early task for developing a complex intervention or evaluating one that has already been developed.
Developing and evaluating complex interventions: the new Medical Research Council guidance
Craig P, Dieppe P, Macintyre S, Michie S, Nazareth I, Petticrew M. Developing and evaluating complex interventions: the new Medical Research Council guidance. Bmj. 2008 Sep 29;337:a1655.
The ToC approach has been successfully used to design, implement and evaluate complex community initiatives, and more recently has been applied to complex health interventions, including at LSHTM. The way a ToC may improve the evaluation of interventions is by combining evaluations of intervention effectiveness with detailed process evaluations into one theoretical framework. The ToC approach to evaluation tests the hypothesised causal mechanisms with what is observed to have happened. This allows identifying which components and activities were strong and effective in achieving the outcomes, and which were weak or absent causing limited effects.
The ToC and logic model are developed in collaboration with stakeholders and draw on various sources of information, including academic theories and evidence from a range of disciplines, program experience, health care provider’s insights and service users and carer insights.
Evaluations based on the ToC have sometimes been referred to as theory-based evaluations. In the following article, the author describes how theory-based evaluation allow an understanding of how programs work by examining how the hypothesised causal mechanisms are occurring in practice, as well as how successfully implementation is achieved.
Theory-based evaluation: Past, present, and future
Weiss CH. Theory‐based evaluation: Past, present, and future. New directions for evaluation. 1997 Dec 1;1997(76):41-55.
In a review by Rogers et al., the authors highlight that this approach of basing an evaluation on a logic, or causal, model is not new and has been recommended by evaluators since the 1960s. They refer to it as the ‘program theory evaluation’ and describe its historical development, the current variations in theory and practice, and discuss the problems it poses.
Program theory evaluation: Practice, promise, and problems
Rogers, P.J., Petrosino, A., Huebner, T.A. and Hacsi, T.A. (2000) Program theory evaluation: Practice, promise, and problems, New Directions for Evaluation, 2000, 87, 5-13.
The following guide provides an orientation to the underlying principles and language of the logic model so it can be effectively used in program planning, implementation, and evaluation. It also offers a range of exercises and examples focused on the development of a logic model that reflects the underlying theory of change.
Logic model development guide
Kellogg Foundation, W.K. (2004) Logic model development guide, Battle Creek, MI: W.K Kellogg Foundation.
The following is another useful guide to developing logic models
Kirby D. BDI logic models: a useful tool for designing strengthening and evaluating programs to reduce adolescent sexual risk-taking pregnancy HIV and other STDs.
ToC can also be used to predict whether interventions might have harmful effects, both to mitigate and evaluate these.
“Dark logic” – theorising the harmful consequences of public health interventions
Bonell C, Jamal F, Melendez-Torres GJ, Cummins S. “Dark logic” – theorising the harmful consequences of public health interventions. Journal of Epidemiology and Community Health 2015;69(1):95-8.
Theory about the mechanisms and contextual factors that may affect them can be quantitatively tested through causal modelling. Mediation analysis is used to examine the hypothesised mechanisms, and analysis of moderation can be used to examine the contextual factors that may influence the effect of the intervention.
A causal modelling approach to the development of theory-based behaviour change programmes for trial evaluation
Hardeman, W., Sutton, S., Griffin, S., Johnston, M., White, A., Wareham, N.J. and Kinmonth, A.L. (2005) A causal modelling approach to the development of theory-based behaviour change programmes for trial evaluation. Health education research, 20, 6, 676-687.
LSHTM’s Centre for Global Mental Health is using Theory of Change in the implementation and evaluation of two major trials:
PRIME (Programme for Improving Mental health carE)
» Using workshops to develop Theories of Change in five low and middle income countries: lessons from the Programme for Improving Mental Health Care (PRIME)
Breuer E, De Silva MJ, Fekadu A, Luitel NP, Murhar V, Nakku J, Petersen I, Lund C. Using workshops to develop theories of change in five low and middle income countries: lessons from the programme for improving mental health care (PRIME). International journal of mental health systems. 2014 Apr 30;8(1):1.
SHARE (South Asian Hub for Advocacy, Research and Education on Mental Health)
» Theory of change: a theory-driven approach to the MRC framework for complex interventions
De Silva MJ, Breuer E, Lee L, Asher L, Chowdhary N, Lund C, Patel V. Theory of Change: a theory-driven approach to enhance the Medical Research Council’s framework for complex interventions. Trials. 2014 Jul 5;15(1):1.
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