How Effective Are Credible Sources in Changing Behavior? A Systematic Review with Meta-Analysis
Jack Hamer1, Tracy Epton1, Danielle Hamer2
1University of Manchester, UK.
Personality & Social Psychology Bulletin
|May 22, 2026
Summary
Credible sources have a small positive effect on behavior. Effectiveness is enhanced when sources are medical professionals, communication is in-person, and interventions are immediate and verbal.
Area of Science:
- Behavioral Science
- Psychology
- Health Communication
Background:
- Understanding factors influencing behavior is crucial.
- Credible sources are often assumed to impact behavior, but empirical evidence needs synthesis.
- Focusing on performed behavior, not just attitudes, offers deeper insights.
Purpose of the Study:
- To systematically review and meta-analyze the effects of credible sources on performed behavior.
- To identify contexts and conditions under which credible sources are most effective.
- To differentiate effects on behavior from effects on behavioral antecedents like attitudes.
Main Methods:
- Systematic review and meta-analysis of 34 papers.
- Searched six databases up to June 2024.
- Analyzed 40 effect sizes from 7,995 participants (58.42% female, mean age 17.75).
Main Results:
- A small, statistically significant positive effect of credible sources on behavior was found (d = 0.14).
- Significant moderators included medical professional qualification, in-person communication, verbal/combined interventions, single occurrence behavior, and immediate post-intervention timing.
- Effect sizes varied based on specific contextual factors.
Conclusions:
- Credible sources exert a small but significant influence on performed behavior.
- The effectiveness of credible sources is context-dependent, with specific characteristics amplifying their impact.
- The cost-benefit of employing credible sources should be carefully considered due to the modest effect size.
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