Because different types of studies have different features, the same validity criteria is not used for all articles. There are different techniques needed to appraise articles of diagnosis, harm/etiology, prognosis, and systematic review.
Key issues for Diagnostic Studies:
diagnostic uncertainty
blind comparison to gold standard
each patient gets both tests
To evaluate the validity of a diagnostic test study, review the following questions:
Did participating patients present a diagnostic dilemma?
The group of patients in which the test was conducted should include patients with a high, medium, and low probability of having the target disease. The clinical usefulness of a test is demonstrated in its ability to distinguish between obvious illness and those cases where it is not so obvious or where the diagnosis might otherwise be confused. The patients in the study should resemble what might be expected in a clinical practice.
Did investigators compare the test to an appropriate, independent reference standard?
The reference (or gold) standard refers to the commonly accepted proof that the target disorder is present or not present. The reference standard might be an autopsy or biopsy. The reference standard provides objective criteria (e.g., laboratory test not requiring subjective interpretation) or a current clinical standard (e.g., a venogram for deep venous thrombosis) for diagnosis. Sometimes there may not be a widely accepted reference standard. The author will then need to clearly justify their selection of the reference test.
Were those interpreting the test and reference standard blind to the other results?
To avoid potential bias, those conducting the test should not know or be aware of the results of the other test.
Did the investigators perform the same reference standard to all patients regardless of the results of the test under investigation?
Researchers should conduct both the study test and the reference standard on all patients in the study regardless of the results of the test in question. Researchers should not be tempted to forego either test based on the results of only one of the tests. Nor should the researchers apply a different reference standard to patients with a negative results in the study test.
Knowledge Check
Read the information on this page then answer the following questions.
Question 1) Why should patients in a diagnostic test study represent a range of probabilities (high, medium, and low) of having the target disease?
A) To simplify data analysis by avoiding diagnostic uncertainty.
B) To demonstrate the test’s ability to distinguish between obvious, uncertain, and confusing cases, similar to real clinical situations.
C) To show that the test performs well only in patients with a clear diagnosis.
Question 2) What is the primary purpose of comparing a new diagnostic test to an independent “gold standard”?
A) To ensure that the new test replaces the gold standard in future studies.
B) To verify that the new test produces results identical to the gold standard every time.
C) To provide an objective benchmark that confirms whether the target disorder is truly present or absent.