Odds Ratio Example

An epidemiologist decides to conduct a Case Control Study by comparing 50 people with lung cancer to 50 people without lung cancer. She investigates the potential causal factor of smoking to find that 45 out of 50 smokers had lung cancer, whereas 5 out of 50 non-smokers had lung cancer. This is graphically depicted below:

The Odds Ratio= (case(+) * control(+))/(case(-) * control(-))

The Odds Ratio for the example above= 45*47/5*3

Conclusion: Since the odds ratio is so high, conclude that smoking is a significant factor in lung cancer.