Odds Ratio Flashcards
A case-control study is designed to investigate whether being exposed to passive smoking as a child is a risk factor for nicotine dependence. Two hundred patients with nicotine dependence are recruited. Of these 200, 40 report either one or both parents smoking in the house when they were a child. A further 200 controls who do not have nicotine dependence are recruited. Of these people 20 report that one or both parents smoked in the house. What is the odds ratio of developing nicotine dependence after being exposed to passive smoking as a child?
The odds of those with nicotine dependence being exposed to passive smoking is 40 / 160 = 1 / 4
The odds of the controls being exposed to passive smoking is 20 / 180 = 1 / 9
The odds ratio is therefore 1/4 / 1/9 = 9/4 = 2.25
