A Brief Guide to the Measures of Impact Used in Epidemiology and Public Health

In epidemiology, to evaluate how strongly a risk factor is associated with a disease, measures of association, such as relative risks and odds ratios, are used. The attributable risk (AR) is related to the relative risk but, while relative risk represents the ratio of the incidence rates, AR is the difference between these rates. Measures of impact such as AR estimate how much of the disease would be prevented if the risk factor was removed from the population. AR is the difference in the disease rates in exposed and unexposed individuals to a risk factor. AR is calculated from prospective data (cohort study) and may be calculated as the difference in cumulative incidences (risk difference) or incidence densities (rate difference), reflecting the absolute excess risk of the disease in the exposed group compared with the non-exposed group. AR quantifies how much the risk in the exposed group is attributable to the exposure. Population attributable risk (PAR) is the incidence of a disease in the population that would be eliminated removing the exposure to a risk factor. PAR is calculated by subtracting the incidence in the unexposed from the incidence in the total population. Population etiological fraction (FEpop.) is the fraction of disease occurrence in the population that would not have occurred if the risk factor had not been present in the population. (Epidemiology_statistics)