Biostatistics & Research · single question
Calculate SPECIFICITY from the given diagnostic table: Disease YES: 3700 positive, 50 negative. Disease NO: 35 positive, 3500 negative.
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Correct answer: D. 99%
Specificity = 99% (D).
Specificity = True Negatives / (True Negatives + False Positives)
= 3500 / (3500 + 35) = 3500 / 3535 = 0.9901 = 99%
• True Negatives (TN) = 3500 (disease NO, test NEGATIVE — correctly identified as disease-free)
• False Positives (FP) = 35 (disease NO, test POSITIVE — incorrectly flagged as diseased)
• Specificity = ability of a test to correctly identify those WITHOUT disease. High specificity = few false positives.
• Sensitivity = TP/(TP+FN) = 3700/(3700+50) = 98.7% ← ability to correctly identify those WITH disease.
• High specificity tests are useful for CONFIRMATION ('rule IN' disease).
Specificity = True Negatives / (True Negatives + False Positives)
= 3500 / (3500 + 35) = 3500 / 3535 = 0.9901 = 99%
• True Negatives (TN) = 3500 (disease NO, test NEGATIVE — correctly identified as disease-free)
• False Positives (FP) = 35 (disease NO, test POSITIVE — incorrectly flagged as diseased)
• Specificity = ability of a test to correctly identify those WITHOUT disease. High specificity = few false positives.
• Sensitivity = TP/(TP+FN) = 3700/(3700+50) = 98.7% ← ability to correctly identify those WITH disease.
• High specificity tests are useful for CONFIRMATION ('rule IN' disease).
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