Article
Toward a better understanding of the influences on physical activity: The role of determinants, correlates, causal variables, mediators, moderators, and confounders

https://doi.org/10.1016/S0749-3797(02)00469-5Get rights and content

Abstract

Background: For research on physical activity interventions to progress systematically, the mechanisms of action must be studied. In doing so, the research methods and their associated concepts and terminology become more complex. It is particularly important to clearly distinguish among determinants, correlates, mediators, moderators, and confounder variables used in physical activity research. This article examines the factors that are correlated with and that may have a causal relationship to physical activity.

Methods and Results: We propose that the term “correlate” be used, instead of “determinant,” to describe statistical associations or correlations between measured variables and physical activity. Studies of the correlates of physical activity are reviewed. The findings of these studies can help to critique existing theories of health behavior change and can provide hypotheses to be tested in intervention studies from which it is possible to draw causal inferences. Mediator, moderator, and confounder variables can act to influence measured changes in physical activity. Intervening causal variables that are necessary to complete a cause-effect pathway between an intervention and physical activity are termed “mediators.” The relationship between an intervention and physical activity behaviors may vary for different groups; the strata by which they vary are levels of “moderators” of the relationship. Other factors may distort or affect the observed relationships between program exposure and physical activity, and are known as “confounders.”

Conclusions: Consistent use of terms and additional research on mediators and moderators of intervention effects will improve our ability to understand and influence physical activity.

Introduction

A range of theories and models has been used to specify variables that are believed to influence physical activity and other behaviors. Researchers test hypotheses derived from theories by (1) examining associations among theoretically derived variables with behavior that help to “understand and predict” the behavior, and (2) evaluating interventions that are designed to modify the influences that are believed to lead to behavior change. There are hundreds of behavioral studies on physical activity, with great diversity in research designs, measurement approaches, populations studied, theories used, variables tested, and physical activity outcomes. This diversity makes it difficult to integrate the findings and summarize the status of the field, thus limiting the ability of subsequent research to build on previous findings.

This paper is divided into several sections, the first describing the criteria for causal relationships, which draws mainly from epidemiologic methods. Definitions are then provided for the key terms and examples are used to illustrate them. The third section deals with correlates of physical activity and how well they are linked to theories of behavior change. The fourth section reflects on these terms from a behavioral science perspective.

It is particularly difficult to integrate the results from associational and intervention studies. Part of this difficulty is due to the inconsistent use of terms and misuse of logical and empiric guidelines for ascertaining and describing causality. The primary aim of this paper is to recommend more standardized use of selected terms related to understanding the causation of physical activity behavior. It is hoped that clarification of terms will contribute to improvements in behavioral research on physical activity, with the explicit goal of enhancing the effectiveness of interventions.

Section snippets

The logic of causality: defining correlates and determinants

Identifying factors that are associated with physical activity is a basic research concern. Many studies have attempted to explain and predict behavior, as well as to test hypotheses derived from specific theories. The research literature on physical activity is replete with findings of significant cross-sectional associations between a range of personal, social, and environmental variables and levels of physical activity. These are usually correlational studies, and might, for example, report

The role of studies on the correlates of physical activity

This section reviews the literature on the correlates of physical activity. These should not be considered as causal factors. Nonetheless, research to identify correlates has both practical and theoretical uses. Practically, correlational studies generate hypotheses about possible causal relationships and about potential mediators that can be targeted in intervention studies. Theoretically, correlational studies could test predictions derived from theory and produce results that eventually lead

Application of mediator and moderator concepts: a behavioral science perspective

This section presents reflections from a behavioral science perspective. The consistent application of mediator and moderator concepts provides a logic to evaluate influencing variables that are not defined within current theories. There are some limitations to studying only the direct outcomes of interventions or naturally occurring variations in environmental or social conditions on behavior.16 First, if no intervention effect was established, then little knowledge was acquired regarding why

Conclusions

This article has focused primarily on definitional issues, with the aim of establishing a clearer conceptual basis for distinguishing between determinants and correlates, and understanding mediators, moderators, confounders, and process variables in physical activity research. We have reviewed the pattern of findings on the relationships with physical activity of variables from the main theories that have been applied to physical activity behavior. In this research literature, the term

Acknowledgements

This study was support in part by grant R01 HD37367 from the National Institutes of Health (received by DAD).

References (28)

  • T. Baranowski et al.

    Mediating variable framework in physical activity interventionsHow are we doing? How might we do better?

    Am J Prev Med

    (1998)
  • L. Mâsse et al.

    Emerging measurement and statistical methods in physical activity

    Am J Prev Med

    (2002)
  • R.J. Shephard et al.

    Exercise as cardiovascular therapy

    Circulation

    (1999)
  • R. Hambrecht et al.

    Effect of exercise on coronary endothelial function in patients with coronary artery disease

    N Eng J Med

    (2000)
  • R.K. Dishman et al.

    Determinants and interventions for physical activity and exercise

  • M.B. Brewer

    Research design and issues of validity

  • K. Rothman et al.

    Modern epidemiology

    (2001)
  • D.T. Campbell et al.

    Experimental and quasi-experimental designs for research

    (1963)
  • H.C. Kraemer et al.

    How do risk factors work together? Mediators, moderators, and independent, overlapping, and proxy risk factors

    Am J Psychiatry

    (2001)
  • R.M. Baron et al.

    The moderator-mediator variable distinction in social psychological researchconceptual, strategic, and statistical considerations

    J Pers Soc Psychol

    (1986)
  • J.F. Sallis et al.

    Behavioral epidemiologya systematic framework to classify phases of research on health promotion and disease prevention

    Ann Behav Med

    (2000)
  • J.F. Sallis et al.

    A review of correlates of physical activity of children and adolescents

    Med Sci Sports Exerc

    (2000)
  • J.F. Sallis et al.

    Ecological models

  • J.F. Sallis et al.

    Physical activity and behavioral medicine

    (1999)
  • Cited by (0)

    View full text