Biostatistics & Research · patient case question
True negatives divided by the sum of true negatives and false positives gives:
Patient case: Reading the evidence
demo: Journal club
chief: The practice is reviewing published evidence before making a purchasing decision and interpreting a set of student examination results.
history: Five dental students scored 64, 56, 48, 66 and 66 on an examination. A trial reports three laser devices, each with a mean difference and a 95 percent confidence interval. A separate paper reports a diagnostic test's performance.
meds: Not applicable.
findings: Laser 1: confidence interval crossing zero into negative values, lowest price. Laser 2, an erbium YAG device: confidence interval entirely above zero, mid price. Laser 3: confidence interval crossing zero, highest price.
Show answer and explanation
Correct answer: C. Specificity
- A. Negative predictive value is true negatives over all negative results, and it too depends on prevalence.
- B. Sensitivity is true positives over the sum of true positives and false negatives. SnNout: a Sensitive test that is Negative rules disease out.
- C. Correct. That ratio is specificity, the proportion of genuinely disease-free people the test correctly identifies as negative. A highly specific test produces few false positives, so a positive result is convincing. The mnemonic is SpPin: a Specific test that is Positive rules disease in.
- D. Positive predictive value is true positives over all positive results, and it varies with disease prevalence.
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