MCAT® ExamCritical Analysis and Reasoning SkillsMedium
A team of researchers is developing a new diagnostic test for a rare genetic disorder. They conduct initial trials and find that the test correctly identifies individuals with the disorder 98% of the time. However, it also incorrectly identifies individuals without the disorder as having it 5% of the time. In this context, the 98% represents which of the following measures of diagnostic accuracy?
- ASensitivity
- BNegative Predictive Value
- CPositive Predictive Value
- DSpecificity
Show answer & explanationAnswer & explanation
Correct answer: A. Sensitivity
Sensitivity (also called the true positive rate) measures the proportion of actual positives that are correctly identified as such. In this case, the test correctly identifying individuals WITH the disorder (actual positives) 98% of the time is a measure of its sensitivity.
Why the other options are wrong
- B. Negative predictive value (NPV) is the probability that subjects with a negative screening test truly don't have the disease. (Incorrect)
- C. Positive predictive value (PPV) is the probability that subjects with a positive screening test truly have the disease. (Incorrect)
- D. Specificity measures the proportion of actual negatives that are correctly identified as such (true negative rate). (Incorrect)
Sensitivity (Diagnostic Test)
The ability of a test to correctly identify individuals who have a particular disease or condition (true positive rate).
- Calculated as True Positives / (True Positives + False Negatives).
- A highly sensitive test has few false negatives.
- Useful for ruling out diseases (SNOUT: Sensitive Negative, rule Out).
Memory trick: Accuracy is like hitting the target, but from different angles.