(A) Relative risk[?]Relative Risk (RR)oRelative risk a ratio of the probability of the event (outcome variable) occurring in the exposed (risk factor) group to the probability of the outcome occurring in a non-exposed (no risk factor) group.Relative Risk =IncidencerateinunexposedgroupIncidencerateinexposedgroup RR=(c+dc )(a+ba ) oThis is used to compare the risk for two groups.oIt gives a measure of the impact of the behaviour or treatment a group is exposed to.oThe non-exposed group is the baseline group which we measure the impact of the behaviour or treatment against.oRelative Risk does not have to be between 0 and 1Relative risk =Riskfornon-exposedgroupRiskforexposedgroup oRelative risk of Heart Disease in an overweight male compared with a non-overweight male=0.145/0.076=1.90oBased on this study overweight men are 1.9 times more likely to suffer from heart disease than non-overweight men.oRelative risk of heart disease in an smoking male compared with a non-smoking male=0.156/0.096=1.63oRelative risk and Odds ratio are important as measures of the strength of association.-Important for deriving casual interferenceoAttributable risk is a measure of how much disease risk is attributed to a certain exposure-Useful in determining how much disease can be prevented.oTherefore:-Relative risk is valuable in etiologic studies of disease-Attributable risk is useful for Public Health Guidelines and PlanningRELATION BETWEEN RELATIVE RISK & ODDS RATIORelative RiskOdds Ratio*. Needs incidence of the disease*. Incidence not for its calculation*. Usually in prospective, cross sectional & clinical trail studies*. Retrospective studies and in cross sectional.*. Demonstrates temporarily*. Good estimate for RR in case of low frequency disease*. OR can over stimulate risk, in rare disease[?]Odds Ratio vs. Relative RiskoBoth compare the likelihood of an event between two groups.oOR compares the relatives odds of an event in each groupoRR compares the probability of an event in each group-More 'natural' interpretation because risk measured in terms of probability.-Cannot always be computed, Can lead to ambiguous interpretations.RR = Prevent when exposed/Prevent when not exposedoRelative risk or risk ratio (RR) is the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.