Guidance

Introduction to logic models

Published 7 August 2018

This guidance was withdrawn on 17 September 2021

For up-to-date guidance see Evaluation in health and wellbeing.

Introduction to logic models

A logic model is a graphic which represents the theory of how an intervention produces its outcomes. It represents, in a simplified way, a hypothesis or 바카라 사이트˜theory of change바카라 사이트™ about how an intervention works. Process evaluations test and refine the hypothesis or 바카라 사이트˜theory of change바카라 사이트™ of the intervention represented in the logic model.

The design of, and terms used in, logic models vary. However, they commonly include aspects which summarise an intervention바카라 사이트™s:

• inputs/resources
• implementation/outputs
• outcomes/impact
• context
• relationships between them

The Medical Research Council (MRC) (Moore and others 2015) outlines the main aspects of an intervention that a logic model should represent to inform evaluation.

1. Implementation refers to how a service or intervention gets delivered and what gets delivered in practice.
2. Mechanisms of impact relate to the mechanisms through which the intervention works and produces changes in the intervention recipients.
3. Outcomes are the changes that the intervention is ultimately trying to bring about for recipients, such as weight loss or diabetes prevention.
4. Context refers to factors external to the intervention that might influence how the intervention operates.

identify, describe and arrange these critical aspects of an intervention to represent how the intervention produces change, with arrows often used to indicate causal relationships between the aspects.

Logic models are useful for evaluation because they can help prioritise and structure data collection and analysis to explore the main aspects of an intervention and relationships between them. These data can be used to help to explain how the intervention works to achieve its outcomes, or sometimes why it does not work.

A logic model might which encourage child-parent discussions about how to eat more healthily as an 바카라 사이트˜implementation바카라 사이트™ aspect, and changing family attitudes towards diet as a subsequent 바카라 사이트˜mechanism of impact바카라 사이트™ aspect, with an arrow indicating a causal relationship between the two.

Based on this logic model, an evaluator might collect programme records and observational data on the quantity, quality and content of the drama sessions delivered to children, and interview families about their changing attitudes towards food (including questions about the causal relationship between the drama sessions and their attitudes towards food). By collecting data on these aspects of the logic model, the evaluator is able to explore main aspects of the 바카라 사이트˜theory of change바카라 사이트™ of the intervention.

Ideally, logic models should be developed during intervention development, or in the early stages of planning an evaluation, so that they can be used to inform the design of the process evaluation and data collection. However, researchers can develop a logic model to describe an intervention at any stage of an evaluation, including retrospectively - for example, the .

How to create a useful logic model

Ideally, process evaluations are 바카라 사이트˜theory based바카라 사이트™ evaluations, where the evaluation is supported by the underpinning theory of how the intervention works (see Process Evaluation section). The logic model should draw on and summarise this theory. In some cases, an intervention manual may also be useful to specify critical aspects related to the implementation/delivery of the intervention in more detail.

Logic models are usually designed by a study team rather than a single researcher. They tend to require multiple perspectives and careful discussion to identify the critical aspects of an intervention, and to consider how they are related. Just as stakeholders such as patients, clients and staff delivering an intervention can contribute to the development of an intervention, stakeholders can also contribute to the construction of a logic model.

Some approaches, such as the emphasise stakeholder involvement, while some other approaches design the logic model with researchers only.

Good logic models share several features

They do not include detail about absolutely everything that happens in an intervention, but summarise the aspects that are critically important in explaining how the intervention produces the changes that it is aiming to achieve. Therefore, it is important when creating a logic model to decide what these critical aspects are.

They ensure, as far as possible, that 바카라 사이트˜implementation바카라 사이트™, 바카라 사이트˜mechanisms of impact바카라 사이트™, 바카라 사이트˜outcomes바카라 사이트™ and 바카라 사이트˜context바카라 사이트™ are separated in a logic model because these are conceptually distinct. An evaluator will probably have different research questions about these different aspects of the intervention and may want to use different methods to answer these questions

They represent the 바카라 사이트˜cause and effect바카라 사이트™ relationships between different aspects of an intervention using arrows.

Their inclusion should therefore be considered carefully; if an arrow is present, the study team should be able to articulate what causal relationship it represents.

They are not just conceptual maps which represent intervention aspects and the relationships between them; they represent a process of change. Therefore, the time order of 바카라 사이트˜cause and effect바카라 사이트™ represented in the logic model is important. Cause always comes before effect. The aspects should be arranged so that the arrows between them show how one aspect (such as delivery of training material) causes a subsequent aspect (such as improved skills).

They will also represent relationships between different aspects as specifically as possible rather than, for example, listing all 바카라 사이트˜implementation바카라 사이트™ aspects and linking this list with one arrow to a list of 바카라 사이트˜mechanisms of impact바카라 사이트™ aspects. This is particularly true for interventions which are large or complex and have many different components, with different theorised mechanisms.

A 바카라 사이트˜list바카라 사이트™ approach in a logic model does not illustrate the causal pathways or theory of the intervention in much detail. Therefore, it will not be useful in guiding the data collection and analysis.

There are also several features of logic model design which are highly variable, depending on the intervention. A good logic model is designed and adapted so that it accurately represents the underpinning theory of the specific intervention, rather than being based on a standard template.

Logic models may include more detail on one aspect of the intervention than others. The following examples demonstrate how this can be true for different aspects.

In some interventions, the implementation process may be complex, involving different stages of staff training and re-organisation of service delivery systems. For this type of intervention, the logic model might include a number of aspects to describe the different aspects and stages of implementation.

In other types of interventions, such as those using mobile phone apps, the implementation process is likely to be much simpler and the logic model would not need to include much detail on this aspect of the intervention. However, the mobile phone app may be designed with multiple 바카라 사이트˜mechanisms of impact바카라 사이트™ (for example, goal-setting, social support, description of behaviour, feedback, and self-monitoring).

Some interventions may only impact on outcomes at one point in time, and this will be represented in the final section of a logic model. In other studies, short, medium and long-term outcomes may all be of interest, and therefore the 바카라 사이트˜outcomes바카라 사이트™ part of the logic model might extend to several sections.

An additional factor to consider relates to the level of intervention. For example, whether the intervention is targeted at an individual, family, organisational or community level, as this will affect the content of the logic model at:

• an individual level: a logic model for an individual level intervention might include detailed aspects describing psychological processes which underpin its mechanisms of impact (such as changes in individuals바카라 사이트™ social identity and attitudes)
• a community level: a logic model for a community intervention would include aspects describing group or community level changes (such as increased participation rates in a local sports facility following a physical activity promotion campaign)

Early development of a logic model is advisable. It helps to focus the process evaluation on the most important research questions and make best use of limited resources for data collection and analysis.

Several researchers who contributed to case studies included in the MRC process evaluation guidance were asked what they would have done differently in their studies. They commented that they would have developed the intervention theory and logic model earlier, to allow them to address the major process evaluation questions in a more focused way.

Limitations of logic models

Logic models tread a fine line between being simple, easy to understand and use, and reflecting the complexity of the real world. A good logic model will include the critical aspects of an intervention that contribute to its outcomes.

In practice, these may be hard to identify in advance, and therefore the logic model may not include every factor that explains outcomes. On the other hand, a very complex logic model may become unwieldy and impractical. The evaluator therefore has the tricky task of finding a balance between these 2 demands.

Logic models have also been criticised for representing interventions as linear and mechanistic, and for overplaying the predictability of an intervention. For example, they tend to give the impression of steady change over time, whereas change may occur in jumps at certain points or problems may initially get worse before they get better.

An alternative perspective comes from 바카라 사이트˜complexity theory바카라 사이트™ which emphasises the unpredictability of processes and characterises interventions as 바카라 사이트˜adaptive바카라 사이트™ rather than fixed systems (Plsek and Greenhalgh 2001).

Logic models could be adapted to a certain extent to accommodate some aspects of complexity theory, such as feedback loops (these are present in the MRC process evaluation framework). However, logic models will remain relatively mechanistic, linear representations of processes of change which do not reflect the full complexity of the real world but, as noted above, provide a simplicity that has advantages for planning and conducting evaluations.

Categorising aspects of logic models

In practice, it can sometimes be tricky to define and agree on which category (such as 바카라 사이트˜implementation바카라 사이트™ or 바카라 사이트˜context바카라 사이트™) an aspect of a logic model falls into. There are no standard definitions for what counts as 바카라 사이트˜implementation바카라 사이트™, a 바카라 사이트˜mechanism of impact바카라 사이트™, 바카라 사이트˜context바카라 사이트™ or 바카라 사이트˜outcome바카라 사이트™ as these will vary depending on the study.

For example, a school may be part of the context for a child bullying intervention which provides counselling for individuals. Alternatively, if an intervention is designed to change the school culture in order to reduce bullying, then the school is part of the intervention not the context.

To decide where aspects of a logic model fit, it can be helpful to think through the intervention in as simple terms as possible.

Implementation

What are the major features that characterise your intervention delivery (for example, what resources and services is the intervention providing; what activities are intervention staff required to undertake; how is the intervention or service delivered)?

Mechanisms of impact

What processes should be triggered by delivery of the intervention (for example, what changes should happen in intervention recipients that wouldn바카라 사이트™t have happened otherwise; how should participants respond to the intervention)?

Outcomes

What are the ultimate aims of the intervention (for example, what changes the intervention is aiming to achieve)?

Context

What external factors may influence the intervention (what is the intervention not addressing; what is beyond the scope of the intervention; what factors in the organisation바카라 사이트™s or participants바카라 사이트™ environment might affect the intervention)?

In addition, difficulties can arise where aspects of the logic model fall into grey areas on the boundaries between categories. For example, patient acceptability may be considered an aspect of 바카라 사이트˜implementation바카라 사이트™ since it reflects on the delivery of the intervention. However, it could also be considered an aspect of how patients respond to and engage with an intervention and, therefore, be included in the 바카라 사이트˜mechanisms of impact바카라 사이트™ category.

Alternatively, a short-term outcome (for example, increased used of a sports facility) could reflect a mechanism of impact in an intervention with an ultimate goal of increasing physical activity. If you are having problems identifying what categories the aspects of your logic model fall into, and if some aspects seem to be on the boundaries, then it can be more useful to concentrate on what the critical aspects of your intervention are.

Concentrate on how they are causally related to each other, rather than getting too caught up in making aspects fit into the 바카라 사이트˜implementation바카라 사이트™, 바카라 사이트˜mechanisms of impact바카라 사이트™ or 바카라 사이트˜context바카라 사이트™ categories exactly.

Developing a logic model for exploratory interventions

If you have designed an intervention, you will have some hypothesis about how it is expected to produce change to resolve the problem you are trying to address. This hypothesis can form the basis of a logic model.

However, there may be some aspects of how the intervention might work or processes that may occur which due to large gaps in knowledge are genuinely unknown. For example, it may be that the intervention is being delivered in a new setting where the contextual factors that could affect the intervention are unknown.

Alternatively, the participant response to the intervention may be very uncertain. In these cases, there may be gaps in logic models which can be specifically explored during the process evaluation with the findings contributing to a more complete logic model at the end of the study.

Useful resources

The following are most relevant to logic models.

Centers for Disease Control and Prevention (2011).

Julia Coffman (1999).

Evaluation Support Scotland (2012).

HM Treasury (2011). 바카라 사이트˜The Magenta Book: guidance for evaluation바카라 사이트™

Health Canada (2013).

Medical Research Council (2006).

Medical Research Council (2014).

National Science Foundation (2002).

NHS Health Scotland (2003).

NHS National Observatory on Obesity (2015).

NHS National Obesity Observatory (2012).

NHS National Obesity Observatory (2012).

NHS National Obesity Observatory (2009).

UN Programme on HIV/AIDS (2008).

US Department of Health and Human Services (2010).

WK Kellog Foundation (2006).

WK Kellog Foundation (2004).

World Health Organization (2013).

Acknowledgements

This work was partially funded by the UK National Institute for Health Research (NIHR) School for Public Health Research, the NIHR Collaboration for Leadership in Applied Health Research and Care of the South West Peninsula (PenCLAHRC) and by Public Health England. However, the views expressed are those of the authors.

Written by Sarah Morgan-Trimmer, Jane Smith, Krystal Warmoth and Charles Abraham.

References

Anderson A (2005). New York: The Aspen Institute roundtable on community change

Coffman J (1999). Harvard Family Research Project

De Silva and others (2014). Trials 15: 267

Evaluation Support Scotland (undated).

Moore, G and others (2014). London: MRC Population Health Science Research Network

Plsek, PE and Greenhalgh, T (2001). British Medical Journal 323: 625-8.

University of Wisconsin바카라 사이트“Extension (undated).

Van Koperen, TM, and others (2013). Obesity Reviews 14 (2): 162-170

WK Kellog Foundation (2004).

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