Measures of Association: Relative Risk and Odds Ratios
Exposure outcome linkages are measured using risk ratios, odds ratios, and impact of exposure on outcomes are measured using impact fractions and population attributable risk percents. Incidence rates are measures of risk in the population. In Environmental Epidemiological cohort studies, two or more incidence rates are compared between those who are not exposed and those who are exposed. The resulting ratio is referred to as incidence rate ratios, or relative risks. Absolute risk refers to the difference between the exposed and non-exposed population in the incidence of the health outcome. Here is an example.
Imagine you are studying the association between ETS and Asthma in primary school-age children and for this purpose you have decided to compare two populations. Population A (N = 200) is exposed to ETS and Population B (N = 300) is not exposed to ETS. You have followed both the populations for five years and have tallied the number of new Asthma cases in those five years among primary school children for both groups. The results of your study are shown in the following table: