. Exposure to a Risk Factor Recent meat Ingestion No recent meat lmrestfon Total Health Status With Enteritis Without Enteritb necrotlcan1 necrotlcans 50 16 11 41 61 57 Usihg the formula for the odds ratio: OR=ad/bc = so (41)/16 (11) = 11,6 Total 66 S2 118 The OR inclicates that the people who were diagnosed to have Enteritis necroticans were u. 6 times more likely to have ingested meat compared to those who were not diagnosed to have the disease. Attributable Risk provides information about absolute effect of the e;,,. l)osure or the e. xcess risk of the di$ease to a causal agent. It gives a better idea tban the RRR of the impact of successfi_1J preventiv e or public hea]th program might have in reducing the problem. It is computed by taking the difference in the incidence rates of disease between e;,,. 'J)osed and non-exposed population. Attributable Risk= Incidence Rate among e11posed-Incidence Rate amon1 the non­ exposed The concept of attributable risk can be shown by looking into lbe relationship of mothers' atlendnnc e to reg1. 1h1r pre-natal clinic visits to maternal complications. The incidence rate of maternal complications among those who regularly attend pre-natal clinic was 53/10,000 live hirtbs compared to those who do not attend pre-natal clinic at 798/10. 000 live births. The AR was computed at 745 which means that 745 excess cases of maternal complications can be attributed lo non-attendance of pregnant women to regular pre-natal clinics. . Analytic Study Designs: Cohort and Case-Contro l Analytic studies employ cohort and case-control study designs to systematically detem1ine whether or not the risk of disease is different for individual s e. xposed or not exposed to a factor of inleres L Cohort studies arc also called follow-up or incidence studies stru·t with the determination of the suspected exposure factor among the study population and ascertaining their disease status later in the study. Coho. rt can be prospective or retrospecti ve. If the prospective eohort will be employed, the measure of clisease frequency lo be used will be the incidence rate. 111e retrospective cohort uses the prevalence rate as measure of disease frequency. The relative risk, odds ratio and attributab le risk are used to measure st Tength of association between disease and suspected factor. The figure 7. 3 (Beagleho le, et al, 1993) shows how the cohort study design is carried out: 197 