Measures of Association Online version Epidemiology - Measures of Association Practice Problems by Kristin Zimmerman 1 In a case control study, 37 cases of diarrhea were reported. Of these 37 cases, 17 people ate rare steaks. Thirty-three controls were selected and out of those, 7 ate rare steaks. Calculate the odds ratio. a 3.2 b 0.23 c 0.27 d 2.2 2 In a case control study, 37 cases of diarrhea were reported. Of these 37 cases, 17 people ate rare steaks. Thirty-three controls were selected and out of those, 7 ate rare steaks. Calculate the risk ratio. a 2.2 b 3.2 c 1.63 d 1.2 3 What does a risk ratio of 1.63 indicate? a An identical risk between the groups. b An increased risk for the exposed group (those in numerator). c A decreased risk for those in the exposed group (those in numerator). d Exposure protects against the health event. 4 People who attended a picnic were interviewed and it was found that 42 of the 87 attendees became ill with salmonellosis. Forty-eight of the attendees ate potato salad and 36 of them became ill. What is the risk ratio comparing the exposed to the unexposed? a 5 b .75 c 2.7 d 4 5 People who attended a picnic were interviewed and it was found that 42 of the 87 attendees became ill with salmonellosis. Forty-eight of the attendees ate potato salad and 36 of them became ill. What is the odds ratio? a 1.5 b .75 c 2.7 d 2.2 6 What does a risk ratio of 1.0 indicate? a An identical risk between the groups. b An increased risk for the exposed group (those in numerator). c A decreased risk for those in the exposed group (those in numerator). d Exposure protects against the health event. 7 What does a risk ratio of 0.65 indicate? a An identical risk between the groups. b An increased risk for the exposed group (those in numerator). c A decreased risk for those in the exposed group (those in numerator). d Exposure protects against the health event. 8 A hypothetical case–control study in which 200 cases of lung cancer were compared to 200 controls regarding their smoking habits showed the following results: Of the people with lung cancer, 135 were smokers. Of the people without lung cancer, 43 were smokers. What are the odds of having lung cancer among those who smoked? a 1.3 b .45 c .76 d 2.75 9 A hypothetical case–control study in which 200 cases of lung cancer were compared to 200 controls regarding their smoking habits showed the following results: Of the people with lung cancer, 135 were smokers. Of the people without lung cancer, 43 were smokers. What is the odds ratio? a 0.9 b 4.5 c 8.2 d 7.6 10 A hypothetical case–control study in which 200 cases of lung cancer were compared to 200 controls regarding their smoking habits showed the following results: Of the people with lung cancer, 135 were smokers. Of the people without lung cancer, 43 were smokers. Find the risk ratio. - What is the first step to solve this problem? a The first step is to divide the incidence of exposed by the incidence of the unexposed. b The first step is to create the risk table. c The first step is to create and complete the 2x2 table. d The first step is to cross multiply. 11 Which value would complete the 2x2 table? a 133 b 103 c 123 d 143 12 Which 2x2 table accurately depicts the situation described: In an outbreak of MRSA among students at a small college, 28 of 157 students residing on the East wing of the dormitory developed MRSA, compared with 4 of 137 students residing on the West wing. a b c d Feedback 1 Remember odds ratio is calculated by cross multiplying the four inner values of the 2x2 table & dividing the products. 2 Remember to calculate risk ratio you divide the incidence rate of the exposed with the incidence rate of the unexposed. 3 A risk ratio greater than 1 indicates that exposure increases the chance of the health event occurring. 4 Remember to calculate risk ratio you divide the incidence rate of the exposed with the incidence rate of the unexposed. 5 Remember odds ratio is calculated by cross multiplying the four inner values of the 2x2 table & dividing the products. 6 A risk ratio of 1 indicates identical risk among the two groups. 7 A risk ratio less than 1 indicates that the exposure is beneficial (prevents the disease). 8 To solve this problem only look at the odds of lung cancer if an individual smokes (lung cancer in smokers divided by total smokers). 9 Remember odds ratio is calculated by cross multiplying the four inner values of the 2x2 table & dividing the products. 10 Before any measures of association can be calculated the 2x2 table should be created. 11 The number of cases of MRSA and students without MRSA in West Wing must add up to the total provided (137). 12 To create 2x2 table, disease status/health event goes along horizontal (positive then negative) and exposure events along vertical edge (exposed then not exposed).
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