false-negative or a false-positive), results should be interpreted in the context of the history, physical findings, and other test results in the individual being tested. It is within this context that the sensitivity and specificity of the "gold standard" test is determined. When the gold standard is not a perfect one, its sensitivity and specificity must be calibrated against more accurate tests or against the definition of the condition. This calibration is especially important when a perfect test is available only by autopsy. It is important to emphasize that a test has to meet some interobserver agreement, to avoid some bias induced by the study itself. Calibration errors can lead to misdiagnosis. Ambiguity Sometimes "gold standard test" refers to the best performing test available. In these cases, there is no other criterion against which it can be compared and it is equivalent to a definition. When referring to this meaning, gold standard tests are normally not performed at all. This is because the gold standard test may be difficult to perform or may be impossible to perform on a living person (i.e. the test is performed as part of an autopsy or may take too long for the results of the test to be available to be clinically useful). Other times, "gold standard" does not refer to the best performing test available, but the best available under reasonable conditions. For example, in this sense, an MRI is the gold standard for brain tumour diagnosis, though it is not as good as a biopsy. In this case the sensitivity and specificity of the gold standard are not 100% and it is said to be an "imperfect gold standard" or "alloyed gold standard". The term ground truth refers to the underlying absolute state of information; the gold standard strives to represent the ground truth as closely as possible. While the gold standard is a best effort to obtain the truth, ground truth is typically collected by direct observations. See also Evidence-based medicine Ground truth Statistical test References Epidemiology Medical tests