SPM – MCQ 78 – Negative predictive value

A diagnostic test for a particular disease has a sensitivity of 0.90 and a specificity of 0.80. A single test is applied to each subject in the population in which the diseased population is 30%. What is the probability that a person, negative to this test, has no disease?
a) Less than 50%
b) 70%
c) 95%
d) 72%

Correct answer : c) 95%

The probability that a person negative to this test has no disease signifies the Negative predictive value of the test.

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4 Comments
  1. Asmita

    A diagnostic test for a particular disease has a sensitivity of 0.90 and a specificity of 0.80. A single test is applied to each subject in the population in which the diseased population is 30%. What is the probability that a person, negative to this test, has no disease?
    a) Less than 50%
    b) 70%
    c) 95%
    d) 72%

    Correct answer : c) 95%

    How to calculate the answer?

  2. Tanish

    Someone kindly post the calculations in a easy to understand method.

  3. SHANKAR

    assume there are 1000 people .so,there are 300 diseased people among them(as it given prevalence 30%)and who doesn’t have the disease is 700.
    so true positve is 270(sensitivity-90%)
    false negative is 30.
    true negative is 560(specificity-80%).
    false positve is 140.
    NEGATIVE PRED; VALUE=(TRUE NEGATIVE/TRUE NEGATIVE+FALSE NEGATIVE)*100
    =(560/560+30)*100
    =94.9%

  4. SHANKAR

    assume there are 1000 people .so,there are 300 diseased people among them(as it given prevalence 30%)and who doesn’t have the disease is 700.
    so true positve is 270(sensitivity-90%)
    false negative is 30.
    true negative is 560(specificity-80%).
    false positve is 140.
    NEGATIVE PRED; VALUE=(TRUE NEGATIVE/TRUE NEGATIVE+FALSE NEGATIVE)*100
    =(560/560+30)*100
    =94.9%