In an investigation to study the effect of smoking on renal cell carcinoma, it is observed that 30 out of 50 patients were smokers as compared to 10 out of 50 control subjects. The odd ratio of renal cell carcinoma associated with smoking will be
Strength of association in a case control study: Case Control study cannot provide with incidences, so Relative risk cannot be calculated; so in case Control study, we calculate &;an estimate of Relative risk&; known as "Odds Ratio" (Cross Product ratio) CORRECT TABLE CONSTRUCTION in a case control study: table will have disease at the top (row) and history of exposure/ risk factor on the left (column). Odds ratio in a 2*2 table for a case control study: Disease present Disease absent Exposure present a b Exposure absent c d Odds Ratio (Cross product Ratio) = ad/bc Thus in the given question, correct table is To Be Constructed First: Renal cell Cancer present (Cases) Renal cell Cancer Absent (Controls ) Exposure to smoking present a b Exposure to smoking absent c d Total a+c b+d Now, total cases of renal cell cancer (a+c) = 50, smoking exposure present(a) = 30 Total controls (b+d) = 50 , smoking exposure present (b) = 10 Therefore, c = = = 20 and , d= = 50-10= 40 Table construction Renal cell cancer present(Cases) Renal cell cancer Absent (Controls ) Exposure to smoking present 30 10 exposure to smoking absent 20 40 Total 50 50 Odds Ratio = ad/bc= 30*40/20 * 10 = 6 Interpretation of Odds ratio = 6; Renal cell cancer cases have 6 times higher odds than controls of having had the history of exposure to smoking. Ref: Park 25th edition Pgno: 81
3
0.33
6
0.16
Epidemiology