Designing studies of diagnostic tests for low back pain or radiculopathy.

New diagnostic tests for the evaluation of patients with low back pain are constantly emerging, but are often not completely evaluated before they become used. Many published studies have a number of biases that tend to exaggerate the estimated accuracy of a diagnostic test. Several key study design features should be considered in such studies: independent comparison of the diagnostic test results with an appropriate "gold standard"; blinded assessment of the new test and the gold standard or competing tests; the reproducibility of interpretation of the test being examined; and the sensitivity and specificity of the test for the final gold standard diagnosis. In addition, evaluations of test accuracy should include patients with a wide spectrum of illness from mild to severe, and the study setting and patient characteristics should be described in detail. Finally, the contribution of a diagnostic test to the overall validity of a full group or sequence of tests should be considered, and, ideally, the effect of the test on actual patient outcomes should be determined.