When calculating PAFs using RRs adjusted for confounding factors, the prevalence of physical inactivity at baseline among cases of the outcome of interest is required. 5 The World Health Organization (WHO) collects data, by country, on the prevalence of physical inactivity in the population using two similar standardized questionnaires (described in a companion paper) the latest data are for 2008. We define “physical inactivity” to be an activity level insufficient to meet current recommendations “physical activity”, sufficient. Thus, we sought prevalence estimates of inactivity for the whole population and unadjusted RRs to estimate PAF using Formula 1, and prevalence estimates of inactivity for cases and adjusted RRs to estimate PAF using Formula 2.Įstimation of prevalence of physical inactivity Because some confounders (e.g., hypertension in CHD, overweight in diabetes) are exacerbated by inactivity, Formula 2 may over-adjust, while Formula 1 can add perspective. Formula 2 is preferred when there is confounding 8 it requires knowledge of the prevalence of the risk factor among persons eventually developing the disease (“cases”) and the adjusted RR. Formula 1 provides an unbiased estimate when there is no confounding of the relationship between the risk factor and disease, and requires knowledge of the prevalence of the risk factor in the population and the RR not adjusted for confounders (crude RR). At least two formulae are available to calculate PAF ( Figure 2).
PAF is related to prevalence of the risk factor and its associated relative risk (RR). Thus, it provides policy makers with useful quantitative estimates of the potential impact of interventions to reduce/eradicate the risk factor. 7, 8 It estimates the proportion of new cases that would not occur, absent a particular risk factor. The population attributable fraction (PAF) is a measure used by epidemiologists to estimate the impact of a risk factor on disease incidence in a population. We focus on the major NCDs recently highlighted by the United Nations as threats to global health: 6 coronary heart disease (CHD) cancer, specifically breast and colon cancers, which are convincingly related to physical inactivity and type 2 diabetes.Ĭoncept of population attributable fraction (PAF) To quantify the impact of physical inactivity on the world’s major non-communicable diseases (NCDs), we estimate how much of these diseases could be averted in the population if those inactive were to become active, as well as how much gain in life expectancy could occur at the population level. 3– 5 Despite this knowledge, a large proportion of the world’s population remains physically inactive. 2 Since then, a large body of evidence has clearly documented the many health benefits of physical activity, summarized in Figure 1. One of the pioneers whose work helped change that tide of popular opinion was Professor Jerry Morris who conducted the first rigorous, epidemiologic studies investigating physical inactivity and chronic disease risk, published in 1953. And, at the time of the 100 th boat race between Oxford and Cambridge in 1954, the Senior Health Officer of Cambridge University conducted a study to investigate the “alleged dangers” of exercise by comparing university sportsmen with “intellectuals”.
During the early twentieth century, complete bed rest was prescribed for patients with acute myocardial infarction.
By the twentieth century, however, a diametrically opposite view-that exercise was dangerous-prevailed instead. Ancient physicians-including those from China in 2600 BC and Hippocrates around 400 BC-believed in the value of physical activity for health.
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