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Population attributable risk: implications of physical activity dose.

PURPOSE
The purpose of this study is to describe the application of population attributable risk estimates in relation to the dose-related benefits or risks of physical activity.


METHODS
Assumptions and limitations of population attributable risk calculations and interpretations are reviewed and evaluated in the context of physical activity dose. Theoretical estimates are developed for several hypothetical situations.


RESULTS
National estimates of population attributable risk may be inaccurate because definitions and measurement techniques applied in physical activity research studies and physical activity prevalence surveys do not correspond. In addition, it is not established whether vigorous or moderate physical activity are independent contributors, sequential categories, or interactive variables in the process of disease reduction. This information is necessary to calculate population attributable risk most appropriately.


CONCLUSION
Estimates of the disease burden of physical inactivity will be improved by two advances in empirical studies: first, the pairing of prevalence and relative risk estimates for nationally representative population-based samples; and second, refined relative risk estimates for various doses of physical activity.