l 196 lnddenat Rate amcng those exposed Relaaw Risk Ratio = Incidence Rate among those not exposed An e.-. :ample cited in Mac Mahon and Pugh (1970) describes the relationship of heavy smoking (defined as smoking of 25 or more cigarettes per day) and incidence of lung cancer among British m:1le physicians from 1951 to 1961. The incidence rate of lung =~among heavy smokers was 2. 27/1000 population.. Among the non-smokers, the incidence rate was only 0. 07/ 1. 000 population. Using the above formu Ja, the RRR is 32. 4. It means that 1he risk of lung cancer among heavy smokers is 32 t. imes greater compared to non-smokers. The odds ratio is similar to relati Ye risk in a way that it establishes tl1e probability of disease development as a result ofbeinge..,q :,osed to a suspected factor. In epidemiologic studies where incidence rate. s or prevalence rates are not available, the oddi:; ratio is used to estimate tlw risk or probability of disease de,·elopmeut. ff the odds ratio is equal to 1. 0. it suggests that the factor is not a risk factor to the dise~'lse or condit:-ion being inv·estigatt>d. (. :-\. nderson and l\1c Farlane, ::1007) To compute for the odds ratio, a cross tabulati on showing the proportion of persons exposed to a suspected factor with or without cilseca. se a. ad proportiou of persons ·who were not exposed to a suspected factor that de Ye]opt'd or did not develop disease. Exposure to a Rlsk Health Status Total Factor With Disease Without Disease Ep1 dtoafactor A 8 a+b Not e,:po,ed to a factor C D c+d Taal a+c b+d a+b+c+d The odds of having the disease when exposed to a suspected factor is represented by a(b in table 7. 6 wb. ile the odds of having the disease when the factor is absent is represen ted by c/d. The odds ratio is computed: TA8LE 7. 6 ODDS RATIO FORMULA 8/b ad Oclds..a. tro---w.-c/d be The use of odds ratio is demonstrated in a case-control study on the associati on of meat consumption ·with enteritis necrotic. ans in Papua New Guinea (Millar et a J, 1985 cited by Beaglehole, et al, 1993) Enteritis necrotica ns is inflammation of the small bowel, usually the jejunum and ileum leading to ulceration and perforation of the small intestine. rt is a fatal type of food poisoning caused by 13-toxin of Clostridium perfri ngens. 