In an investigation to study the effect of smoking on renal cell cancer, it is observed that 30 of the 50 patients were smokers as compared to 10 out of 50 control subjects. The odd's ratio of renal cancer associated with smoking will be:

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 X 40/20 X 10= 6 Interpretation of Odds ratio = 6 i.e Renal cell cancer cases have 6 times higher chance of repoing history of exposure to smoking as compared to healthy people in the study. Odds ratio is a/k/a Cross product Ratio. Used in case control study.