Study Design — MCQs

Question 121: A case-control study is conducted to investigate the association between the use of phenytoin during pregnancy in women with epilepsy and the risk for congenital malformations. The odds ratio of congenital malformations in newborns born to women who were undergoing treatment with phenytoin is 1.74 (P = 0.02) compared to newborns of women who were not treated with phenytoin. Which of the following 95% confidence intervals is most likely reported for this association?

• A. 0.36 to 0.94
• B. 1.75 to 2.48
• C. 0.56 to 1.88
• D. 0.83 to 2.19
• E. 1.34 to 2.36 (Correct Answer)

Explanation: ***1.34 to 2.36*** - A **95% confidence interval** that does not include **1.0** indicates a statistically significant association, consistent with the given **p-value of 0.02** (which is less than 0.05). - This interval contains the **point estimate (odds ratio of 1.74)**, making it the most plausible range for the true effect. - The confidence interval must always encompass the point estimate from which it is derived. *0.36 to 0.94* - This confidence interval is **entirely below 1.0**, suggesting a protective effect, which contradicts the given odds ratio of **1.74** indicating an increased risk. - This interval does not contain the point estimate of **1.74**. *1.75 to 2.48* - While this interval indicates an increased risk and does not include 1.0, it **does not contain the stated odds ratio of 1.74**, as its lower bound is 1.75. - A confidence interval must always encompass the point estimate from which it is derived. *0.56 to 1.88* - This confidence interval **includes 1.0**, which would imply no statistically significant association between phenytoin use and congenital malformations. - This contradicts the given **p-value of 0.02**, which indicates statistical significance. *0.83 to 2.19* - This confidence interval **includes 1.0**, suggesting **no statistically significant association**. - This contradicts the given **p-value of 0.02**, which demonstrates statistical significance.