In a study there were 35 cases of lung carcinoma and 82 controls were there. On taking history, 33 cases had positive history of smoking and 55 individuals among controls had positive history of smoking. What is the odds ratio-

Ans. is 'a' i.e., 8 * Odds ratio is cross product of entries in the table.* So, it is very important to make a correct table construct -i) History of exposure (risk factor) is arranged on left column (row).ii) Disease is arranged on the top -a) Cases in middle column (row)b) Controls in right column (row) Disease Present (cases)Absent (controls)Exposure presentabExposure absentcdTotala + cb + dComing to question* Cases# Total cases = 35# Among these smokers = 33 (a)# Non smokers = 35 - 33 = 2 (c)* Controls# Total = 82# Smokers = 55 (b)# Non smokers = 82 - 55 = 27 (d)This data can be arranged - Lung cancerPresent (cases)Absent (controls)Smoking present3355(a)(b)Smoking absent227(c)(d)Total35(a + c)82(b + d) Odds ratio ==ad----bc =33 x 27--------55 x 2= 8.1