Odds ratio vs. relative risk — MCQs

Q: A research team conducts a case-control study examining the relationship between smoking and lung cancer. They identify 200 patients with lung cancer (cases) and 200 matched controls without lung cancer. Among cases, 160 were smokers and 40 were non-smokers. Among controls, 80 were smokers and 120 were non-smokers. Calculate the odds ratio for this study.

6.0. ***6.0*** - The **odds ratio (OR)** is calculated for this **case-control study** using the cross-product formula (ad)/(bc), resulting in (160 cases exposed × 120 controls unexposed) / (80 controls exposed × 40 cases unexposed). - Completing the calculation (19,200 / 3,200) yields **6.0**, which means the odds of lung cancer are 6 times higher among smokers than among non-smokers. *2.0* - This value is mathematically incorrect and would only be reached if the **unexposed controls** (120) and **unexposed cases** (40) were ignored or misidentified in the formula. - An OR of 2.0 indicates a much weaker relationship between the **risk factor** and the disease than the study data demonstrates. *4.0* - This result might occur if a student incorrectly divides the **number of smokers in cases** (160) by the **number of smokers in controls** (80) without considering the non-smokers. - This ignores the fundamental definition of **odds**, which involves a ratio of the probability of an event occurring to it not occurring. *8.0* - This value is an overestimation and does not correspond to the product of the **contingency table** cells provided in the scenario. - It represents an error in either the **placement of values** in the 2x2 table or a calculation mistake in the multiplication phase. *10.0* - This value is significantly higher than the actual **cross-product ratio** and is not supported by the ratio of smokers/non-smokers in either group. - Such a high OR would imply a nearly **exclusive association** that is not reflected by the presence of 40 non-smoking cases and 80 smoking controls.

A research team conducts a case-control study examining the relationship between smoking and lung cancer. They identify 200 patients with lung cancer (cases) and 200 matched controls without lung cancer. Among cases, 160 were smokers and 40 were non-smokers. Among controls, 80 were smokers and 120 were non-smokers. Calculate the odds ratio for this study.

Practice by Chapter

Definition and calculation of odds ratio

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Definition and calculation of relative risk

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Interpretation differences

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When odds ratio approximates relative risk

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Common misinterpretations

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Application in different study designs

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Adjusted odds ratios

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Confidence intervals for OR and RR

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Reporting in medical literature

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Absolute risk vs relative measures

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Number needed to treat relation

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Meta-analysis of odds ratios and relative risks

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