American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Paired t tests are used under which circumstance?

1. Comparing two different populations

2. Analyzing two related samples

3. When dealing with more than two groups

4. For independent groups

The correct answer is: Analyzing two related samples

Paired t tests are specifically designed for situations where you have two related samples. This scenario often arises when measurements are taken from the same subjects under two different conditions or at two different times. For example, if a group of patients is measured for blood pressure before and after treatment, the readings are related because they come from the same individuals; therefore, a paired t test appropriately accounts for the correlation between the paired observations. The primary aim of a paired t test is to determine whether there is a statistically significant difference in the means of the two sets of related observations. By focusing on the differences between paired observations rather than treating them as independent, the paired t test increases the statistical power of the analysis while also controlling for within-subject variability. In contrast, the other options relate to situations where paired t tests are not suitable. Comparing two different populations typically requires an independent samples t test. Analyzing more than two groups often calls for ANOVA rather than a paired t test. Lastly, using paired t tests for independent groups is inappropriate, as this method benefits from the related nature of the samples rather than treating them as separate entities.