ABSTRACT
Studies that look at the ability of a test to predict the presence or absence of a disease are called diagnostic studies.
Diagnostic studies are a type of prospective experimental study. Often in this type of study, the researchers look to compare a new test against an established test to see how the new test performs. The test being investigated is termed the ‘index’ test, and the test it is compared to is called the ‘reference’ or ‘gold’ standard. However, it is worth highlighting that although a diagnostic study often uses one individual index test versus one reference test (e.g. ultrasound versus CT aortogram for looking for an abdominal aortic aneurysm [AAA]), the ‘tests’ used may be a combination of clinical features (e.g. hypotension, pain radiating to back, presence of pulsatile mass and over 65 years old) or an individual test with the addition of clinical features (hypotension, pain radiating to back, presence of pulsatile mass and over 65 years old plus ultrasound). This concept is equally applicable to the gold standard as it is to the index test.
