“A meta-analysis of the effectiveness of health belief model variables in predicting behavior” Carpenter, 2010 Natalie Linton Oregon State University October 9, 2014
What is the Health Beliefs Model (HBM)? • Developed by the U.S. Public Health Service in the 1950s • Based in value-expectancy theory measles http://xkcd.com/51/
What is a meta-analysis? • Statistical methods for contrasting and combining results from different studies • Meta-analyses can identify: • patterns • sources of disagreement Previous HBM meta-analyses: • Janz & Becker 1984 • barriers, benefits, susceptibility • did not estimate mean effect sizes • Harrison et. al. 1992 • retrospective studies = larger effect sizes than prospective • did not correct effect size estimates • Zimmerman & Vernberg 1994 • HBM prediction weak compared to Social Cognitive Theory and TRA • did not examine the effects of each variable on behavior
Why did Carpenter conduct a meta-analysis of the HBM? • Determine whether measures of HBM concepts could longitudinally predict behavior • Which elements are strong predictors? • What are the moderators? • Moderators found: • Time between variable measurement (Time 1) and outcome behavior measurement (Time 2) • Type of outcome behavior: • Prevention or treatment • Drug-taking or not drug-related
Methodology • 18 studies (2,702 subjects); published 1982-2007 • Looked at only the first 4 concepts of HBM: • Susceptibility (18), severity (17), barriers (17), benefits (15) • Studies had to include at least 2 of the 4 • Studies had to be longitudinal • Time 1: measure HBM variables • Time 2: measure health-related behavior outcome • Outcome dichotomizedas treatment (8 studies) or prevention behavior (10 studies) • Outcome also dichotomized as drug-taking behavior (5 studies) or other behavior (13 studies)
Perceived susceptibility • Usually not correlated with health behavior (weakest predictor) • Estimates mostly homogenous • Subset of drug-taking studies only set for which susceptibility was positively correlated with behavior • Moderator: length of time • Longer periods of time between Time 1 and Time 2 associated with weaker effects • r = -0.50
Perceived severity • “There is something about about considering complying with a prescription to take drugs that causes people to consider the severity of the consequences for not taking the drugs more so than for other health behaviors” • Moderator: length of time • Severity ratings more likely to be positively correlated to behavior if the behavior is measured shortly after Time 1 • r = -0.37
Perceived benefits and barriers • Strongest predictors of behaviors • Stronger when dealing with preventive behavior • Findings mostly consistent with previous literature • Moderator for perceived benefits: length of time • Longer periods of time between Time 1 and Time 2 associated with weaker effects r = -0.59 http://xkcd.com/388/
Limitations • Small number of studies • Not enough articles providing effect sizes • Variety and varying quality of measures used • 16 (of 18) articles relied on convenience samples • Did not test more complex models that are possible and would be better to test (studies would have needed to report full correlation matrices)
Levels of Causation Ultimate CULTURAL SOCIAL BIOLOGY/ Causes ENVIRONMENT SITUATION PERSONALITY 1 2 3 4 5 6 a f Social/ Personal Nexus c d e b Sense of Information/ Interpersonal Others’ Social Interactions w/ Self/Control Opportunities Bonding Beh & Atts Competence Social Instit’s Distal Influences 7 8 9 10 11 12 g r p i q h k n m l j o Expectancies & Evaluations Self Skills: Motivation Perceived Values/ Knowledge/ Determination Social+General to Comply Norms Evaluations Expectancies 13 14 15 16 17 18 s x ATTITUDES SOCIAL SELF-EFFICACY u w v t Affect and Cognitions TOWARD THE NORMATIVE BEHAVIORAL BEHAVIOR BELIEFS CONTROL Proximal 19 20 21 Predictors Decisions A G B H C I D E F 22 K Experiences 23 Related Behaviors J Intrapersonal Stream Social/Normative Stream Cultural/Attitudinal Stream Biological/Nature Nurture/Cultural DECISIONS/INTENTIONS Trial Behavior EXPERIENCES: Expectancies -- Social Reinforcements -- Psychological/Physiological
Discussion • Why do you think Carpenter found perceived susceptibility to have almost no relationship to health behavior? • Why do you think time between measures worked as a moderator for susceptibility, severity, and benefits? • Why was time between measurements not a moderator for barriers?
References • Christopher J. Carpenter (2010): A Meta-Analysis of the Effectiveness of Health Belief Model Variables in Predicting Behavior, Health Communication, 25:8, 661-669. • DiClemente, R.J., Salazar, L.F., & Crosby, R.A. (2013). Health Behavior Theory for Public Health: Principles, Foundations and Applications. Jones and Bartlett, Boston, MA. • TTI slides provided to H 571 class at Oregon State University.