The Massachusetts General Hospital Handbook of Neurology

Authors: Flaherty, Alice W.; Rost, Natalia S.

Title: Massachusetts General Hospital Handbook of Neurology, The, 2nd Edition

Copyright 2007 Lippincott Williams & Wilkins

> Table of Contents > Medicine > Epidemiology

Epidemiology

A. Sensitivity

The probability that a test will be positive if the condition it tests for is present: Sens = (true positives)/(true positives + false negatives).

B. Specificity

The probability that a test will be negative if the condition it tests for is absent: Spec = (true negatives)/(true negatives + false positives).

C. Bayes' theorem

The likelihood of a pt. having a condition given a positive test result (i.e., the positive predictive value, PV⁺) depends on the frequency (f) of the condition in the population. PV⁺ = (f)(Sens)/[(f)(Sens) + (1 - f)(1 - Spec)]