Base-Rate Fallacy False Positive Share

Problem

For a disease with prevalence prevalence and a test with the given sensitivity and specificity, return the fraction of positive tests that are false positives:

share = (1 - prevalence) * (1 - specificity) / (prevalence * sensitivity + (1 - prevalence) * (1 - specificity)).

Return 0.0 when the denominator is 0 or inputs are invalid.

Hint

Even a good test produces many false positives when the disease is rare.

Test cases

case 1

in: [0.01,0.99,0.99]

expected: 0.5000000000000002

case 2

in: [0.001,0.99,0.99]

expected: 0.9098360655737706

case 3

in: [0.5,0.9,0.9]

expected: 0.09999999999999998

Starter codePython

def false_positive_share(prevalence, sensitivity, specificity):
    # Your code here
    pass

3 test cases · run your code against them in the editor