Evidence of an increased risk of lung cancer associated with cigarette smoking was sought by Doll and Hill. In one study, 649 lung cancer cases were matched by age, and gender to 649 controls; 647 of the cases and 622 of the control had a history of smoking cigarettes.
a. Name the type of study. Case control study
b. Create the appropriate 2X2 table for the study.
Lung Cancer Controls
Smokers 647 622
Nonsmokers 2 27
Total 649 649
c. Calculate the appropriate measure of association for the study.
d. Interpret the results.
c. To calculate the measure of association for the study, we can use the odds ratio (OR). The formula for calculating the odds ratio is (ad/bc), where a is the number of cases exposed (smokers), b is the number of cases unexposed (nonsmokers), c is the number of controls exposed, and d is the number of controls unexposed.
In this case, a = 647 (cases exposed), b = 2 (cases unexposed), c = 622 (controls exposed), and d = 27 (controls unexposed).
Using the formula, the odds ratio is (647*27) / (2*622) = 41569 / 1244 = 33.40
d. The interpretation of the results would be that there is a strong association between smoking cigarettes and lung cancer. The odds ratio of 33.40 indicates that individuals who smoke cigarettes have a significantly higher risk of developing lung cancer compared to those who do not smoke cigarettes.
c. The appropriate measure of association for this study is the odds ratio (OR).
d. To interpret the results:
- The odds of being a smoker among lung cancer cases were 647/2 = 323.5 times higher than the odds of being a smoker among controls.
- This indicates a strong positive association between smoking cigarettes and the risk of developing lung cancer.
- It suggests that smokers are significantly more likely to develop lung cancer compared to nonsmokers in this study.
- These findings support the hypothesis that cigarette smoking is associated with an increased risk of lung cancer.