Chapter 9Measure of EffectAbsolute effects Relative effectsRisk differencePopulation risk differenceRelative riskEtiologic fractionPopulation etiologic fraction- Relative risk= Iexposed /Inonexposed- Risk difference= Iexposed - Inonexposed- Population risk difference- measures the benefit to the population by modifying a risk factor.o Overall rate (Ip) – Inonexposed - Etiologic fraction- proportion of disease in the exposed group that is due to the exposureo (Iexposed – Inotexposed) / Iexposed o (RR-1)/RR- Population etiologic fraction- the effect of removing an exposure on the burden of the populationo (Ip-Ine)/Ipo Pe(RR-1)/Pe(RR-1)+1o Pe=prevalence of exposure500 subjects enrolled in a study. 125 smoke, 375 do not. 25 of the smokers were diagnosed with lung cancer. 15 of the non-smokers were diagnosed with lung cancer. Calculate the risk difference.Disease StatusExposure status?Yes No Totals Incidence rateYes 25 100 125 25/(125)= .2No 15 360 375 15/(375)= .04Relative risk= 0.2/0.04= 50Risk difference= 0.2 - 0.04 = 0.16Etiologic fraction= (0.2-0.04)/0.2 =