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Question 690
Statistics → Epidemiology
Classification
Question
SSBAQuestion Header
Statistics
Question Stem
A screening test gives 180 true-negative results and 20 false-negative results. What is the negative predictive value?
Options
A
10%
B
80%
C
90%
D
95%
E
98%
Explanation
Negative predictive value is the probability that a person with a negative test is genuinely free of the condition. It is calculated as true negatives divided by true negatives plus false negatives. Therefore NPV = 180/(180 + 20) = 180/200 = 90%.
Option Validity
A) 10% is the false-negative proportion among the negative results in this example.
B) The calculation gives 90%, not 80%.
D) A value of 95% is not obtained from the supplied numbers.
E) A value of 98% is not obtained from the supplied numbers.
Further Reading
Saxena - MRCOG-1 Basic Sciences, Chapter 10: Epidemiology/Statistics, Printed p.288.