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:
|
Disease |
No Disease |
|
| Test Positive |
a
true positives |
b
false positives |
| Test Negative |
c
false negatives |
d
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 |