Use of peer-based interventions to facilitate health-related behavior changes in adults is increasing around the world, but the effectiveness of this type of intervention has not yet been systematically evaluated. Our systematic review is the first to examine the effect of peer-based interventions on health-related behavior outcomes in adults.
We analyzed 25 different studies to assess the effectiveness of peer-based interventions in promoting health-related behavior changes in adults. We identified 3 distinct models of peer-based interventions: dyads, groups, and a combination of both. Subgroup analyses by intervention model did not reveal significant differences in outcomes. The majority (72%) of studies employed the dyad model, perhaps because it is the simplest to implement. This model allows the peers to individualize the intervention to meet participants’ needs. It allows for flexibility with participants’ schedules and logistical concerns. It can also facilitate a more personal bond between a participant and peer leader, increase the peer’s legitimacy with the participant, and increase the participant’s willingness to sustain the proposed behavior. Nevertheless, it is difficult to analytically control for these factors, and the wide variation in results reported by studies of this type of intervention limited our analysis of the model’s effectiveness.
Analysis of outcome groups showed that the studies in 3 of the 7 groups had significant positive findings (increasing physical activity, decreasing smoking, and increasing condom use). One study reported significantly increasing advance directive completion. These are desirable health outcomes that will positively affect the health of individual participants, their families, and the public health care system. The success of peer-based interventions in producing these outcomes suggests that they may be effective for other outcomes.
However, the evidence is mixed. For the remaining 4 outcomes (breastfeeding, medication adherence, women’s health, and participation in general activities), the studies we analyzed did not report a significant difference between participants exposed to the peer-based intervention and members of the control group. This may be related to the variability among interventions that we grouped together because of their similar outcomes of interest; for example, the training and experience level of the peers may have varied, which could lead to varied results. The dose of the interventions also varied in the studies we grouped together. Among the breastfeeding intervention studies, for example, the peers spent from 16 minutes to more than 2 hours with the participants. This variability in dose may have led to the heterogeneity among the studies.
Our systematic review had several strengths, including the use of explicit eligibility criteria, reviewers who independently assessed eligibility, and a random-effects analytic model. We included only randomized clinical trials to help eliminate confounding from other variables. Yet, even when studies used similar intervention models and outcomes, we found little standardization. We used subgroup analyses to explore the effect of the varied intervention models, follow-up times, settings, training of peer leaders, and doses of intervention among the different studies but did not detect any variables that could explain the differences in outcomes.
The main limitation of our review was our use of study quality as an exclusion criterion. To address concerns about study rigor, 2 reviewers assessed quality with a standardized instrument. Quality-rating scores are controversial, but only 18 of 909 studies were eliminated from the analysis because of low quality scores.47
We used this score to limit our analysis to more generalizable studies. For example, 1 study that was excluded had a sample size of 8. Other excluded studies did not explain how the investigators collected their data or which instruments they used.
Another limitation was the heterogeneity of some outcomes. Health behavior change theories contend that it is appropriate to combine the varied behavior change outcomes, but the statistical assumptions of systematic reviews suggest otherwise. We found significant heterogeneity in our overall analysis and among some of our grouped outcomes. Although it is possible that much of this heterogeneity is related to the clinical diversity of the studies, we did not have enough evidence to confirm this, which limited our ability to answer our primary research question: are peer-based interventions effective in changing health-related behaviors in adults? Subgroup analyses did not reveal the source of the heterogeneity but did eliminate variables such as intervention model, intervention setting, sample size, and publication year. However, future research might alleviate this problem by using a commonly agreed-upon definition of peer-based intervention and a common evaluation protocol, including follow-up time.
Most of the outcomes were ascertained by self-report. The nature of behavior change renders it difficult to efficiently assess by other methods, but self-reporting should be complemented with a direct measure of behavior change whenever possible. Complementary outcomes in various studies we analyzed could have included, for example, pediatric disease rates, changes in weight, HIV viral control, or cancer rates, but few reported such outcomes. The low prevalence of such outcomes may make adequately powered sample sizes difficult to assemble, but future research would be enhanced by inclusion of such clinical outcomes or an accepted proxy in their protocols.
We were unable to assess the effect of the dose of intervention on behavior outcomes because each study reported dose differently, in ways that could not readily be compared (e.g., some reported the number of sessions but not total time spent). A great strength of peer-based interventions is their flexibility, which can be applied to real-world problems, but the variability in both dose and how it was reported precluded quantitative statistical analysis of the studies we reviewed. We recommend that future studies report dose in standardized units of time so that the effects of dose can be determined.
Health-related behavior changes are increasingly important because many health conditions are becoming more chronic and less susceptible to biomedical interventions. It is therefore important to learn more about how large numbers of people can be induced to modify their activity level and decrease unhealthy behaviors.
Our systematic review showed that peer-based interventions facilitated positive outcomes, but evidence was mixed. The studies reported significant effects on physical activity, smoking, and condom use but no significant effects on breastfeeding, medication adherence, women’s health, or participation in general activities. Evaluation of the effectiveness of peer-based interventions would be facilitated by future research conducted with rigorous methods, including the quantification of dose in time.