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


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.
School of Community Medicine and Public Health, University of New South Wales, Sydney, Australia. a.bauman@unsw.edu.au
Adrian E
AE
Bauman
James F
JF
Sallis
David A
DA
Dzewaltowski
Neville
N
Owen
D001525:Behavioral Sciences; D015984:Causality; D002755:Choice Behavior; D015986:Confounding Factors, Epidemiologic; D015438:Health Behavior; D006293:Health Promotion; D006801:Humans; D010809:Physical Fitness; D012107:Research Design