- Research article
- Open Access
- Open Peer Review
The effectiveness of community engagement in public health interventions for disadvantaged groups: a meta-analysis
© O'Mara-Eves et al.; licensee BioMed Central. 2015
- Received: 19 December 2013
- Accepted: 5 January 2015
- Published: 12 February 2015
Inequalities in health are acknowledged in many developed countries, whereby disadvantaged groups systematically suffer from worse health outcomes such as lower life expectancy than non-disadvantaged groups. Engaging members of disadvantaged communities in public health initiatives has been suggested as a way to reduce health inequities. This systematic review was conducted to evaluate the effectiveness of public health interventions that engage the community on a range of health outcomes across diverse health issues.
We searched the following sources for systematic reviews of public health interventions: Cochrane CDSR and CENTRAL, Campbell Library, DARE, NIHR HTA programme website, HTA database, and DoPHER. Through the identified reviews, we collated a database of primary studies that appeared to be relevant, and screened the full-text documents of those primary studies against our inclusion criteria. In parallel, we searched the NHS EED and TRoPHI databases for additional primary studies. For the purposes of these analyses, study design was limited to randomised and non-randomised controlled trials. Only interventions conducted in OECD countries and published since 1990 were included. We conducted a random effects meta-analysis of health behaviour, health consequences, self-efficacy, and social support outcomes, and a narrative summary of community outcomes. We tested a range of moderator variables, with a particular emphasis on the model of community engagement used as a potential moderator of intervention effectiveness.
Of the 9,467 primary studies scanned, we identified 131 for inclusion in the meta-analysis. The overall effect size for health behaviour outcomes is d = .33 (95% CI .26, .40). The interventions were also effective in increasing health consequences (d = .16, 95% CI .06, .27); health behaviour self-efficacy (d = .41, 95% CI .16, .65) and perceived social support (d = .41, 95% CI .23, .65). Although the type of community engagement was not a significant moderator of effect, we identified some trends across studies.
There is solid evidence that community engagement interventions have a positive impact on a range of health outcomes across various conditions. There is insufficient evidence to determine whether one particular model of community engagement is more effective than any other.
- Community engagement
- Community participation
- Community development
- Systematic review
- Theoretical model
- Public health
Historically, interventions and actions to promote health were driven by professionals with little or no input from the targeted populations . A more recent movement from practitioners, policymakers, and researchers has been to engage members of the community in public health interventions (e.g., [2,3]). Community engagement has been broadly defined as “involving communities in decision-making and in the planning, design, governance and delivery of services” ( p 11). Community engagement activities can take many forms and are usually described in terms of five levels of engagement (from least to most engaged): information-giving, consultation, joint decision-making, acting together, and supporting independent community interests .
Community engagement has been advocated as a potentially useful strategy to reduce health inequalities (e.g., [6-8]). Health inequalities are evident where disadvantaged groups (e.g., people with low socioeconomic status, socially excluded people) tend to have poorer health than other members of society . Importantly, health inequalities refer to differences in modifiable health determinants, such as housing, employment, education, income, access to public services, and personal behaviour (e.g., use of tobacco), as opposed to fixed determinants such as age, sex, and genetics. Given that the social determinants of health are potentially modifiable, community engagement interventions to reduce health inequalities have been implemented and evaluated. There are, however, few investigations of whether intervention effects can be directly attributed to the community engagement strategy—most evaluations differ between the intervention and control conditions in more ways than just the engagement of community members.
Previous reviews of the community engagement literature suggest potential social improvements but unclear effects on morbidity, mortality and health inequalities [6,9]. An international literature review for the World Health Organisation found that participatory empowerment has been linked to positive outcomes such as social capital and neighbourhood cohesion for socially excluded groups . However, the author noted that links to health outcomes are more difficult to identify. Similarly, Popay et al.’s rapid review  found some evidence for improvements in social capital, social cohesion, and empowerment as a result of community engagement, but little evidence of improvements for mortality, morbidity, health behaviours, or impact on inequalities. The authors found that no studies evaluated the effect of community engagement on outcomes directly, and that evaluations were often carried out too soon in the intervention lifecycle to demonstrate impact.
In summary, it seems that community engagement is likely to have a positive effect on social inequalities [6,9], which might in turn reduce health inequalities , although the direct effect on health inequalities is still uncertain [6,9]. This review attempted to examine both direct and indirect pathways to reducing health inequalities through community engagement approaches, by taking a broader approach to the literature than previous reviews and through the use of innovative search processes to identify the dispersed evidence.
Design and definitions
This paper presents the results of a statistical analysis that is one component in a broader project (reported in a). The full project was a multi-method systematic review containing four components in addition to the meta-analysis presented here: a map of the evaluative and theoretical literature that describes the scale and range of community engagement interventions; a thematic summary of process evaluations linked to evaluation studies focused on health inequality policy priority areas; an analysis of costs and resources; and a newly developed conceptual framework that brings together the learning from all components of the project. An advisory group that consisted of expert academics and practitioners helped to guide the conceptual focus of the review, including the decision about what studies to include in the meta-analysis.
We use several key terms in this paper. A ‘community’ is a group of people with some common, identified feature, such as geographical location or a socio-demographic characteristic [11,12]. An ‘engagee’ is a member of the community that is involved in the identification, design, and/or delivery of the intervention; engagees are distinct from the intervention ‘participants’, who receive the intervention. The intervention ‘deliverer’ is the person who delivered the intervention, regardless of their status as an engagee or professional .
Aims and research questions
Do public health interventions that engage members of the community improve health-related outcomes (health behaviours, health consequences, self-efficacy, perceived social support, and community outcomes)?
Are different approaches to engagement differentially effective?
Do certain features of the interventions (health topic, universal versus targeted approach, intervention setting, intervention strategy, intervention deliverer, and duration of the intervention) moderate intervention effectiveness?
Are certain features of the participants (health inequality category, age) related to intervention effectiveness?
Do features of the evaluation impact observed effectiveness (i.e., is there a risk of bias)?
Study identification and selection for the meta-analysis
The search syntax strategies used are presented in Appendix A and the detailed screening and inclusion criteria are recorded in the full project report  and in a methodology paper . Here we briefly summarise the process which differed from many systematic reviews, because the concepts that we were searching for (i.e. community engagement and inequalities) were not always central concerns of the studies we were looking for – and hence would not appear systematically in their titles, abstracts or keywords. In order to overcome this, we identified systematic reviews of public health interventions, and utilised the structured information in their evidence tables to find relevant studies for our review. Electronic searches thus focused on the identification of systematic reviews (from which we identified primary studies), and electronic searches for primary studies were less extensive than would usually be the case. We estimate that more than a quarter of the studies we included would have been missed using traditional search techniques .
We searched the following sources without language restriction for systematic reviews of public health interventions: Cochrane CDSR and CENTRAL, Campbell Library, Database of Abstracts of Reviews of Effects, NIHR Health Technology Assessments programme website, Health Technology Assessments database, and the Database of promoting health effectiveness reviews (DoPHER). Through the identified systematic reviews, we collated a database of primary studies that appeared to be relevant and screened the full-text documents of those primary studies against our inclusion criteria. In parallel, we searched the NHS EED and TRoPHI databases for primary studies which may not have been included in any existing systematic reviews. We also contacted key authors and conducted citation searching of included studies to identify further studies.
Reported primary research;
Were not a Masters thesis;
Included intervention outcome and/or process evaluations;
Focused on community engagement as the main approach;
Contained a control or comparison group;
Characterised study populations/reported differential impacts of social determinants of health according to the ‘PROGRESS-Plus’ framework : Place of residence, Race/ethnicity, Occupation, Gender, Religion, Education, Socio-economic position, and Social capital, Plus other variables describing ways in which people may be systematically disadvantaged by discrimination (including sexual orientation, disability, social exclusion, and challenging life transitions such as teenage pregnancy); and
Reported health or health-related (including cost) effectiveness outcomes and/or process data.
Due to the large number of studies identified for inclusion in the map of community engagement interventions (n = 319; see full report for details), and in order to align our work with policy priority areas, we narrowed the scope of health topics included in the meta-analysis by focusing on the policy objective areas identified in the Marmot Review of health inequalities, ‘Fair Society, Healthy Lives’ , which assembled evidence and advised the Department of Health, England on the development of a health inequalities strategy, plus the key modifiable health risks identified in the Marmot Review (smoking, alcohol abuse, substance abuse, and obesity). This led to a final sample of 131 studies.
Data were extracted on models, approaches, and mechanisms of community engagement; health topic; participant characteristics; geographical and contextual details; costs and resources; and processes (the full data extraction tool is included in the report, ). To ensure consistency in interpretation and to minimise error, data extraction was undertaken by researchers working independently in pairs, and then meeting to discuss and resolve any disagreements.
Effect size estimates for participants and engagees (where available) were calculated using standard techniques , adjusting for cluster allocation  where necessary. Effect size estimates based on continuous data were calculated as the standardised mean difference (represented by d), while logged odds ratios were used for binary outcomes. Logged odds ratios were transformed to standardised mean differences using the methods described in Lipsey and Wilson  so that the different types of effect size estimates could be included in the same analysesc. A positive d indicates that participants in the treatment group, on average, scored higher than those in the control group. An effect size estimate of d = 1.0 means that participants in the treatment group scored – on average – one standard deviation higher than the control group on the particular outcome measure.
Health behaviours. Outcomes extracted were: alcohol abuse, antenatal (prenatal) care, breastfeeding, cardiovascular disease, child illness and ill health, drug abuse, healthy eating, immunisation, injury/safety, parenting, physical activity, smoking cessation, smoking/tobacco prevention, and other captured above
Health consequences. Outcomes extracted were: cardiovascular disease, child abuse prevention, child illness and ill health, healthy eating, hypertension, injury/safety, mental health, obesity/weight status, and other not captured above
Participant self-efficacy pertaining to the health behaviours
Participant social support in relation to the health behaviours
Community outcomes (e.g. ‘local area improved in the last 3 years’)
Engagee outcomes (e.g. physical activity levels or health knowledge of the engagee)
Studies could contribute more than one effect size estimate to the dataset under the following conditions:
Where there were both immediate post-test and delayed follow-up measures, in order to test the persistence of effects over time; and/or
Where there were outcomes from more than one of the six outcome types listed above (NB. only one outcome from each of the above categories was extracted); and/or
Where there were measures of both engagees and public health intervention participants.
As a result, we calculated multiple effect size estimates for some studies: a total of 212 across the 131 studies. Of the 212 effect size estimates, 191 were calculated from post-test measurements and 21 were from follow-up measurements. This paper refers only to the 191 post-test effect size estimates unless otherwise stated; the follow-up measures are only explored in terms of long-term outcomes in the section ‘Maintenance of intervention effects’. Of the post-test effect size estimates, 81 studies (42.4%) only contributed one effect size estimate, and the mean number of effect size estimates per study was 1.77 (SD = .79).
There were sufficient data to undertake statistical analyses for all outcomes except community and engagee outcomes, which are presented in tabular format. The results (effect sizes and standard errors) of individual studies are presented in forest plots by outcome category.
We conducted random effects model analyses (ANOVAs and multiple regressions) with maximum likelihood estimators, following the methods described in . We used SPSS macros written by David Wilsond to run the models. For the homogeneity analyses, between groups Q-statistic (QB) indicates the extent to which the categories of studies differ from each other; and within groups Q-statistic (QW) indicates the extent to which the effect size estimates within a category differ from each other. Analyses were conducted separately for post-test measures and follow-up measures. Analyses were also conducted separately for the different outcome categories (health behaviours, health consequences, self-efficacy, and social support). As such, each study only contributed one effect size estimate to each analytical model.
Theory of change underpinning the intervention
Single or multiple components to the intervention
Universal versus targeted approach
Duration of the intervention
Age of participants
Controlled trials were assessed for methodological quality using a modified Cochrane risk of bias assessment tool which is reproduced in Appendix B . An overall risk of bias grading of ‘high’ or ‘low’ was assigned on the basis of assessments of three subscales: selection bias, attrition bias, and selective reporting bias. For a study to be classified as ‘overall low risk of bias’, all three types of bias had to be avoided. In addition to the overall risk of bias, the type of comparison group and the randomisation of participants to conditions were assessed in separate random effects ANOVAs as potential methodological features that might affect the observed effect size estimate; these analyses were conducted separately for each outcome type.
Sample size. An un-weighted regression analysis with sample size as a predictor variable was conducted to try to explain heterogeneity in the dataset.
Direct versus indirect comparisons of community engagement. Most interventions were compared to a comparison condition that differed from the intervention in more ways than just community engagement. For example, they might present a completely alternative intervention, or use a waitlist/delayed treatment control condition. We call these indirect comparisons. Direct comparisons are those in which the only difference between the treatment conditions was the presence or absence of community engagement; e.g., one study  compared peer with non-peer led health education using the same healthy eating programme materials. We conducted an ANOVA to compare mean effect sizes of these two types of comparisons.
Health outcome type. A further concern relates to the breadth of health topics and health outcomes included in the sample of studies, which we combine in the analyses under the umbrella of ‘health behaviour outcomes’. As such, we tested the difference between outcome types (breastfeeding, health service use, healthy eating, physical activity, substance abuse, tobacco use, and other health behaviours).
Finally, we considered the possibility of publication bias. Concerns about publication bias have been raised after observations that research evaluations showing beneficial and/or statistically significant findings are more likely to be published than those that have undesirable outcomes or non-significant findings . If this phenomenon does occur, then reviews of a biased evidence base will draw biased conclusions. Unfortunately, it is difficult to assess publication bias because there is no way of knowing the extent of what has not been published. In this review, the risk of publication bias was assessed visually using a funnel plot with the effect size estimate on the x-axis and the estimate’s standard error on the y-axis.
We identified 943 records of potentially relevant systematic reviews, 81 of which were duplicate records. Of the 862 unique records, 622 were excluded during assessment of titles and abstracts. Full text copies of 240 systematic reviews were obtained and assessed for eligibility. Seven of these subsequently did not meet minimum methodological standards to be regarded as systematic reviews, and a further forty-two reviews did not include any relevant primary studies. The 7,506 primary studies from the remaining 191 systematic reviews were examined for relevance, an average of 39 studies per review, within a range of three to 547. This process identified 988 eligible studies, all of which were retrieved and re-assessed against our inclusion criteria on the basis of a full-text report.
We also searched TRoPHI and NHS EED databases for reports of primary studies directly, and came across other eligible studies (through recommendations from colleagues or email alerts) before and while working on the review, resulting in 1,961 titles and abstracts to screen after duplicate checking. On the basis of their titles and abstracts, the full texts of 163 of these records were retrieved.
Description of the studies included in the meta-analysis
We present here a summary of the key characteristics of the studies included in this analysis. Full details of all these studies, with a detailed breakdown of the risk of bias assessment, can be found online at reference .
Of the 131 studies included in the meta-analysis, 113 (86.3%) were conducted in the USA, five (3.8%) were conducted in the UK, five (3.8%) were conducted in Canada, and eight (6.1%) were conducted in other OECD countries. In terms of publication date, 63 (48.1%) were published in the 1990s, 62 (47.3%) in the 2000s, and 6 (4.6%) in 2010 or later.
The largest group of studies was classified as being primarily targeted at or delivered to ethnic minority groups (n = 56, 42.7%), followed by socioeconomic position (n = 34, 26.0%). There was also a large group of studies (n = 21, 16.0%) that had multiple PROGRESS-Plus categorisations; the majority of these represented a combination of ethnic minority group status with low income and/or inner-city status. Most of the ethnic minority participants were classified as either ‘Black’, African American, or ‘Hispanic/Latino’.
The studies included a spread of participants across all age groups and most included participants from more than one age group. The majority of the studies (n = 79; 60.3%) included young people (age 11–21 years) and/or adults (age 22–54 years; n = 65, 49.6%). For sex, 79 (60.3%) studies had mixed sex samples, 49 (37.4%) had predominantly female samples, and three (2.3%) had predominantly male samples.
The interventions and their evaluation
The interventions were conducted over a range of health topics and settings. The most commonly-targeted health issue was substance abuse (n = 18, 13.7%), followed by cardiovascular disease (n = 14, 10.7%), breastfeeding (n = 13, 9.9%), obesity prevention / weight reduction (n = 13, 9.9%), smoking cessation (n = 12, 9.2%, public health/health promotion (n = 8, 6.1%) and antenatal care (n = 7, 5.3%). The most common setting for interventions was in the community (n = 56, 42.7%). Many interventions were also conducted via media tailored to the participants’ needs (e.g., tailored newsletters or information sheets, n = 53, 40.5%) or mass media (n = 21; 16%); such interventions could be delivered wherever the participant was located.
Most of the interventions included multiple intervention strategies. The most common strategy was education provision (n = 105, 80.2%). Advice (n = 71, 54.2%), social support (n = 58, 44.3%), and skill development training (n = 51, 38.9%) were also common strategies. Interventions were most commonly delivered by peers (n = 49, 37.4%) and by community members (n = 58, 44.3%).
A variety of comparators were used in the intervention evaluations. The largest group of evaluations employed usual care comparators (n = 39, 30%); followed by inactive control (n = 31, 24%), alternative/placebo intervention (n = 28, 21%), waitlist/delayed treatment (n = 16, 12%), matched data from target population (n = 10, 7%), and other/unclear (n = 7, 5%). Thirteen (10%) of the studies examined the effectiveness of community engagement by having a comparison condition that only differed from the intervention by the involvement of community members; for example, an intervention that had the same content but was delivered by a peer in the intervention condition and a health professional in the comparison. Fifty-nine (45%) evaluations used randomisation methods to allocate participants to the intervention or comparison condition. Twenty-six (19.8%) of the evaluations conducted follow-up testing.
Risk of bias within studies
The risk of bias assessment of the 131 included studies is presented in Additional file 1. On this basis, sixty-nine (52.7%) trials were considered to have an overall low risk of bias and 62 (47.3%) trials were considered to have an overall high risk of bias.
Results of individual studies
Results of analyses according to each review question
We now move to the main focus of the results: addressing each of our review questions. We begin with an examination of our overarching question – whether community engagement interventions improve health-related outcomes. We then look to see whether some approaches to community engagement work better than others, whether they work better in some groups than others, and finally examine the relationships between sample size and outcome reported.
Do public health interventions that engage members of the community improve health-related outcomes?
Outcomes description, effect size estimates, and their standard errors for engagee and community outcomes
Binary data (logged odds ratios)
Government [ 20 ]
Local area improved in the last three years
Fried [ 21 ]
More physical activity at post-test
Fried [ 21 ]
Engagee Social support/capital/inclusion
Could have used more emotional support from others in the past year
Continuous data (standardised mean differences)
Ernst [ 22 ]
Connection with health and social services
Watkins [ 23 ]
Lay health workers knowledge
Winkleby [ 24 ]
Perceptions that advocacy activities would result in changes
Pooled effect size estimates and heterogeneity for four types of outcomes – random effects model
Pooled effect size estimate
Participant social support
Table 2 presents the results for the outcomes: health behaviours, health consequences, participant self-efficacy, and participant social support. The pooled effect size estimate across interventions is positive (indicating that the outcomes measured were in favour of the treatment group) and statistically significant (as indicated by the p-values and 95% confidence intervals) for these four outcomes. The statistical significance of the pooled effect means that the effect size estimate is significantly different from a null effect in which there are no differences between the intervention group and the comparison group.
There was, however, significant heterogeneity across the four categories of quantitative outcomes observed in Table 2. As such, we conducted moderator analyses to attempt to explain variation in the observed effectiveness of the interventions. These analyses are described in the following sections, but first we examine whether intervention effects lasted beyond the immediate post-test measurement.
Maintenance of intervention effects
The maintenance of intervention effects could only be synthesised for health behaviour outcomes because of the lack of follow-up data reported for other outcome types. The pooled effect size estimate at delayed follow-up for the twenty studies that reported health behaviour follow-up outcomes was d = .09 (95% CI = −.23, .34), although significant variation (I2 = 94.43%) suggests that the pooled estimate is not particularly meaningful.
We conducted a meta-regression analysis to attempt to explain the variation. We included post-test effect size estimate as a predictor, so that any variation in the follow-up effect size estimates due to initial intervention effectiveness could be accounted for. We also included the time between the post-test and follow-up measures as a predictor.
Results of the random effects meta-regression analyses examining follow-up effect size estimates
Predictor of follow-up effect size estimate
Post-test effect size estimate
Less than a year since post-test measure
Are different approaches to engagement differentially effective?
Theories of change
We ran an analysis to compare the effectiveness of interventions employing one of four different theories of change on health behaviour outcomes, identified in the conceptual synthesis of the broader project (10). The first model proposes that change is facilitated where the health need is identified by the community and they mobilise themselves into action. In the second model, the need for intervention is usually identified by observation from people outside the community, but the views of stakeholders are sought with the belief that the intervention will be more appropriate to the participants’ needs as a result. We identified two main mechanisms through which stakeholder views are sought in the design or planning of the intervention: through collaboration with the community, or through consultation with the community. These two mechanisms are treated as separate models in the analysis. The fourth theory of change model does not necessarily involve the community in the design or planning of the intervention; rather, the focus is on community engagement in the delivery of the intervention (we refer to these throughout this paper as lay-delivered interventions). In this model, change is believed to be facilitated by the credibility, expertise, or empathy that the community member can bring to the delivery of the intervention.
Results of the random effects ANOVA analyses by theory of change for health behaviour outcomes
Theory of change
Pooled ES estimate
Average sample size (SD)
Community identified health need
Collaboration to design more appropriate intervention
Consulted to design more appropriate intervention
Lay-delivered to enhance credibility, expertise, or empathy
We conducted supplementary analyses to try to explain why the lay-delivered interventions might be more effective. One explanation that we considered was the size of the study. We suspected that the lay-delivered interventions tended to be smaller-scale and usually more likely to be one-on-one, compared to interventions where the community was involved in the design of the intervention. From Table 4, we can see that the mean sample size for studies that only involved the community in the delivery of the intervention is much smaller than in studies based on alternative theories of change. Post hoc analyses of a one-way ANOVA with sample size as the dependent variable and the different theories of change as the factors indicate that the mean sample size for the lay-delivered interventions is statistically significantly smaller than for the interventions in which the community identified the health need.
Single and multiple component interventions
There is only one component to the public health intervention, which involves community engagement in some way
There are multiple components to the public health intervention, all of which involve community engagement in some way (whether through design, delivery, or evaluation)
There are multiple components to the public health intervention, only some of which involve community engagement in some way (whether through design, delivery, or evaluation)
Results of the random effects ANOVA analyses by community engagement in one or more components of the intervention for health behaviour outcomes
Components in intervention
Pooled ES estimate
Only one component
All components involve CE
Only some components involve CE
Do certain features of the interventions moderate intervention effectiveness?
We explored a range of characteristics of the interventions, to better understand which types of interventions work best when communities are engaged. The characteristics examined were: health topic, universal versus targeted approach, intervention setting, intervention strategy, intervention deliverer, and duration of the intervention. These variables were selected as they cover key features affecting intervention design, implementation, and resourcing.
Modifiable health risks (smoking, alcohol abuse, substance abuse, and obesity)
Best start in life (antenatal care, breastfeeding, parenting skills, and childhood immunisation)
Prevention of ill health – topics not captured above (healthy eating, physical activity, general health promotion, injury prevention, cancer prevention, and CVD/hypertension prevention)
Results of the random effects ANOVA analyses by Marmot themes for health behaviour and health consequences outcomes
Marmot review theme
Pooled ES estimate
Health behaviours a
Best start in life
Prevention of ill-health and injury
Health consequences b
Best start in life
Prevention of ill-health and injury
There were sufficient data to undertake this analysis for health consequence outcomes as well. As with health behaviours, the difference between the three categories was non-significant, although there was a trend in which interventions targeting the best start in life had a smaller pooled effect size estimate than those targeting ill health prevention, which in turn had a smaller pooled effect size estimate than those targeting the modifiable health risks. In contrast to health behaviour outcomes, only the health risks category had a pooled effect size estimate that was significantly different from zero for health consequences outcomes. In other words, there was no evidence that interventions targeting best start in life or the prevention of ill-health had a significant impact on health consequence outcomes.
Universal versus targeted approach
Results of the random effects ANOVA analyses comparing universal and targeted interventions for health behaviour outcomes
Universal or targeted
Pooled effect size estimate
Results of the random effects ANOVA analyses comparing interventions conducted in community settings with non-community settings for health behaviour outcomes
Pooled effect size estimate
Not community setting
Results of the random effects meta-regression analyses comparing intervention strategies for health behaviour outcomes
Mean effect size estimate
Skill development or training
Access to resources or services
Results of the random effects meta-regression analyses comparing different intervention deliverer types for health behaviour outcomes
Mean effect size estimate
Results of the random effects meta-regression with peer and community intervention deliverers as predictors of intervention effectiveness for health consequences outcomes and self-efficacy
1.70 (p = .43)
.58 (p = .75)
The reverse trend is apparent for self-efficacy outcomes: interventions delivered by community members are associated with smaller effect size estimates. Again, intervention deliverer was not a significant predictor of self-efficacy effect size estimates.
Duration of the intervention
We tested whether the duration of the intervention was associated with the effect size estimates for health behaviours, health consequences, and self-efficacy outcomes. Because duration was not normally distributed, we used two approaches to testing this variable. For health behaviour outcomes, the data were normalised using a logarithmic transformation. For health consequences and self-efficacy outcomes, the data were still non-normal after log transformation, and so we created a categorical variable of short, medium, and long duration interventions.
Results of the random effects meta-regression with duration of the intervention as a predictor of health behaviour outcomes
Results of the random effects ANOVA analyses comparing intervention duration categories for health consequences and self-efficacy outcomes
Pooled ES estimate
Health consequences a
Less than 6 months
6 Months to 23 months
2 or more years
Participant self-efficacy b
Less than 6 months
6 Months to 23 months
2 or more years
Are certain features of the participants (PROGRESS-Plus group, age) related to intervention effectiveness?
Results of the random effects ANOVA analyses by PROGRESS-Plus group for health behaviour outcomes
Pooled ES estimate
'At-risk' or 'high risk' young people, including pregnant/parenting teenagers
Place of residence
Multiple health inequalities
Results of the random effects ANOVA analyses comparing interventions targeted at different age groups for health behaviour outcomes
Age groups targeted
Pooled ES estimate
Children or young people (0–17)
Young people and adults (11–54)
Do features of the evaluation (risk of bias) impact observed effectiveness?
We explored the potential risk of bias by considering three methodological features of studies: the type of comparison group, randomisation of participants to conditions, and the overall risk of bias of the study. As described in the methods section, overall risk of bias is a combined measure of the degree of risk of bias on the three subscales: selection bias, attrition bias, and selective reporting bias.
Homogeneity results for different potential risk of bias variables on four outcome types
Risk of bias variable
Between groups Q
Within groups Q
Comparison group type
7.71 (p = .26)
97.14 (p = .51)
.14 (p = .93)
95.60 (p = .63)
Overall low risk of bias
1.27 (p = .26)
97.45 (p = .64)
Comparison group type
Overall low risk of bias
.18 (p = .67)
36.66 (p = .44)
Comparison group type
Overall low risk of bias
1.68 (p = .19)
20.33 (p = .31)
Comparison group type
Overall low risk of bias
.04 (p = .85)
7.19 (p = .21)
We tested whether there was a difference between studies that directly tested community engagement compared with indirect comparisons. Two important features are relevant to determining whether it makes sense to combine these outcomes: the between group heterogeneity statistic and the direction of each subgroup’s pooled effect size estimate. The results of the analysis were not statistically significant (which was unsurprising given the small number of studies with direct comparison evaluation approaches; QB (1) = .01, p = .93). The group means suggest no trends in either direction: the pooled effect size estimate was .34 for studies with a direct comparison and .33 for indirect comparisons. This analysis suggests that including both direct and indirect comparisons in the analyses is not likely to be a source of bias.
We also tested the difference between outcome types (breastfeeding, health service use, healthy eating, physical activity, substance abuse, tobacco use, and other health behaviours). The between-group heterogeneity statistic indicates that the groups are not statistically significantly different from each other (QB (6) = 12.27, p = .06). The pooled effect size estimate for each group is statistically significantly different from zero in the positive direction. Although there is some variation in the magnitude of effects, these results do not suggest that we should be concerned about combining these outcomes in the analyses on the basis of statistical differences.
Risk of publication bias
In Figure 7, the effect size estimates are plotted against their standard errors for both continuous and binary outcomes. From the figure, we can see that larger effect size estimates (in terms of magnitude) typically have larger standard errors; that is, larger effects are associated with more variability. This can indicate a potential for publication bias.
We believe, however, that our sampling frame may help protect us from publication bias. By identifying studies primarily through systematic reviews that have taken measures to protect against publication bias (e.g., searching grey literature), our set of studies includes many reports that would not be subject to the presumed publication bias associated with journal articles.
Overall, public health interventions using community engagement strategies for disadvantaged groups are effective in terms of health behaviours, health consequences, health behaviour self-efficacy, and perceived social support. These findings appear to be robust and not due to systematic methodological biases. The small group of studies that measured longer term outcomes were heterogeneous, although effects generally are smaller than at post-test. There are also indications from a small number of studies that community engagement interventions can improve outcomes for the community and engagees.
We caveat these overall statements with the observation that there is significant variation in the intervention effectiveness; some interventions were more effective than others, and not all interventions benefited the participants. We tested a set of pre-determined variables that we hoped might explain this variance and address the research questions posed. Unfortunately, very few of these variables were statistically significant in explaining differences between interventions.
We were unable to test the hypothesis that community engagement can reduce health inequalities through their impact on social inequalities due to insufficient data. In support of previous research and proposals [6,8,9], however, there was some evidence to suggest that community engagement interventions improve social inequalities (as measured by social support in seven studies: d = .41, 95% CI .23, .65).
We compared the effectiveness of interventions based on four different theories of change in the synthesis of effectiveness data. The results suggest that lay-delivered interventions tend to have larger effects than interventions based on empowerment or patient/consumer involvement, although this trend did not significantly explain variation in the effectiveness across studies. We propose that this association is likely to be confounded with other factors, such as intervention intensity and exposure (lay-delivered tend to be more intense, one-on-one or small group interventions, than other intervention types). For such models, we might expect to see large effects over a narrow range of outcomes, as opposed to the other theories of change models that might have smaller effects over a broader range of health and social outcomes. Unfortunately, there were insufficient data to test these relations adequately. Indeed, community engagement interventions often operate in non-linear pathways (synergies between various components and multiple outcomes) which makes evaluation complicated (compared to, for example, simple dose–response relationships). In order to assess the potentially diverse impacts of community engagement interventions, researchers need to incorporate a spectrum of outcome measures and plan long-term evaluations. Moreover, primary studies should conduct thorough process evaluations and conduct qualitative research to complement these types of evaluations as they can elucidate the ‘active ingredients’ of the intervention (and potential un-intended effects).
Interventions that engage community members in the delivery of the intervention are particularly effective (compared with interventions that empower the community or involve members in the design of the intervention).
Single component interventions tend to be more effective than multi-component interventions for health behaviour outcomes.
Both universal and targeted interventions are effective, although universal interventions tend to have higher effect size estimates for health behaviour outcomes.
Interventions that employed skill development or training strategies, or which offered contingent incentives, tended to be more effective than those employing educational strategies for health behaviour outcomes.
Interventions involving peers, community members, or education professionals tended to be more effective than those involving health professionals for health behaviour outcomes.
Shorter interventions tended to be more effective than longer interventions for health behaviour outcomes, although this is probably confounded by levels of exposure or intensity of contact with the intervention deliverer.
Interventions tended to be most effective in adult populations and less effective in general populations (i.e. those that included all age groups) for health behaviour outcomes.
Interventions tended to be most effective for health behaviour outcomes for participants classified as disadvantaged due to socioeconomic position (compared with those targeted to people on the basis of their ethnicity, place of residence, or being at/high risk). Interventions targeting participants on the basis of place of residence do not appear to be effective for health behaviour outcomes.
Issues arising from the breadth of this review topic
This was a challenging review to undertake due to the breadth of research and perspectives it contains. As well as crossing multiple topic domains, there are also differing perspectives regarding the nature of community engagement and what should count as a community engagement intervention. Political issues loomed large, with some papers arguing for particular solutions from utilitarian and ethical positions. We navigated this uneven landscape by structuring our analysis according to the theories of change which underpin the interventions, thus transcending differences in both health topic and politics, and focusing on the intervention mechanisms which, in some situations, bring about a change in outcomes. While clinical and situational heterogeneity was inevitable and unavoidable, our conceptual framework afforded us homogeneity at the theoretical level, and any claims to generalizability must also be considered at this level (rather than, for example, probabilistic predictions).
Such broad reviews take considerable time and resource, and while there is an inevitable delay between when the searches were carried out (2011) and eventual publication, we do not think this necessarily undermines the currency of the findings presented. The theories of change around which our analyses are structured are based on enduring concepts around community engagement, some of which date from half a century and more ago. We have no reason to believe that community engagement as a theory and as a practice has undergone a fundamental shift since these theories were developed. Moreover, even if a radically new approach has been tested in a small number of studies, any effects would need to be implausibly large – as would the studies themselves – to be able to change the results of our meta-analysis (given that it is based on more than 100 studies). We are therefore confident that the results of this analysis will remain valid for many years to come.
Issues in interpreting statistical findings
Significant statistical heterogeneity was expected in this review, and indeed the exploration of this heterogeneity was part of its design. When operating across such a wide range of topics, populations and intervention approaches, however, there is a disjunction between the conceptual heterogeneity implied by asking broad questions and the methods for analysing statistical variance that are in our ‘toolbox’ for answering them.
First, analysing the variance ‘explained’ by specific sub-groups of studies according to our conceptual framework rarely reached accepted standards for statistical significance. This is inevitable however, because conceptual homogeneity was never achieved through such a sub-division: each type of approach to engagement was observed across populations, topics, outcomes and a wide range of other unknown variables; we would therefore never reach the position of being able to say that the studies within a given sub-group differed only due to sampling error/variance. (Or that any of our sub-divisions was the only way of partitioning the studies present.) In other words, potential confounding variables or interactions amongst variables made it difficult to disentangle unique sources of variance across the studies. Second, the use of statistical significance testing in meta-analysis has itself been questioned as lacking a sound statistical basis [25,26]. While defending the practice, Mark Lipsey states that the magnitude of effect size estimates should be given greater weight in meta-analysis than the results of tests for statistical significance (and observes that if such statistical testing is wrong for meta-analysis, then it is almost certainly incorrect for most social scientific research) .
In the context of our analysis these debates have a clear relevance, because statistical tests for significance are unlikely to yield statistically significant findings, due to complex heterogeneity in the dataset. We are therefore left with an interpretive challenge: do we adhere strictly to the p > 0.05 convention before accepting that a given sub-group analysis is meaningful; or do we place more importance on the magnitude of the differences of effect size estimates between sub-groups? In this review we have attempted to plot a path somewhere between the two extremes. We have tested and reported statistical significance, but have also drawn tentative conclusions from the directions and magnitudes of effects whether or not standard statistical significance had been achieved.
A further issue for the statistical synthesis in this review relates to the comparators used in the evaluations. In the vast majority of interventions synthesised in the meta-analysis (118 out of 131; 90%), interventions were compared to a comparison condition that differed from the intervention in more ways than just community engagement. The lack of a ‘pure’ comparator in most community engagement interventions in this review could cloud our interpretation of the findings. Although we conducted a sensitivity analysis of this issue and found no difference between studies with ‘pure’ comparators versus contaminated comparators, we are unable to conclude definitively that community engagement is the ingredient necessary for intervention success. More evaluations in which community engagement is the only difference between comparison conditions are required to determine the added value of community engagement.
There is solid evidence that community engagement interventions have a positive impact on a range of health and psychosocial outcomes, across various conditions. There is insufficient evidence to determine whether one particular model of community engagement is most likely to be more effective than any other.
aProtocol available at http://www.phr.nihr.ac.uk/funded_projects/pdfs/PHR_PRO_09-3008-11_V01.pdf.
bNote that the research questions have been reorganised compared to the full report to facilitate presentation as a stand-alone research paper.
cWe conducted a sensitivity analysis to test whether d effect size estimates based on binary data were statistically similar to d effect size estimates based on continuous data. Although pooled binary outcomes tended to be slightly smaller than pooled continuous outcomes, this difference was not statistically different (QB (1) = 3.03, p = .08).
eAn un-weighted model, in which the weight for all studies was set to 1, was used because including study weights in the model would inflate the observed relationship between sample size (the independent variable) and effect size (the dependent variable). This is because the inverse variance study weights used in meta-analysis are largely a function of sample size.
David McDaid, Tihana Matosevic, and Angela Harden, for their contributions to the full project, and Katherine Twamley, Irene Kwan, Carol Vigurs, and Jenny Woodman who helped with screening and/or document retrieval.
This report refers to independent research commissioned by the National Institute for Health Research (NIHR). Any views and opinions expressed herein are those of the authors and do not necessarily reflect those of the NHS, the NIHR, the PHR programme, or the Department of Health.
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