17.1 - Analysis of Diagnostic Tests

To begin, let's consider a simple test which has only two possible outcomes, namely, positive and negative. When a test is applied to a group of patients, some with the disease and some without the disease, four groups can result, as summarized in the following 2 × 2 table:



No Disease

Test Positive
true positives
false positives
Test Negative
false negatives
true negatives

a (true-positives) = individuals with the disease, and for whom the test is positive

b (false-positives) = individuals without the disease, but for whom the test is positive

c (false-negatives) = individuals with the disease, but for whom the test is negative

d (true-negatives) = individuals without the disease, and for whom the test is negative

a + c = total number of individuals with the disease

b + d = total number of individuals without disease

The "Gold Standard" is the method used to obtain a definitive diagnosis for a particular disease; it may be biopsy, surgery, autopsy or an acknowledged standard. Gold Standards are used to define true disease status against which the results of a new diagnostic test are compared. Here are a number of definitive diagnostic tests that will confirm whether or not you have the disease. Some of these are quite invasive and this is a major reason why new diagnostic procedures are being developed.

Target Disorder Gold Standard
breast cancer excisional biopsy
prostate cancer transrectal biopsy
coronary stenosis coronary angiography
myocardial infarction catheterization
strep throat throat culture