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Commentary on: Lockhart JJ, Satya‐Murti S. Diagnosing crime and diagnosing disease: bias reduction strategies in the forensic and clinical sciences. J Forensic Sci 2017;62(6):1534–41.

Sir, I read the article regarding cognitive bias by Drs. Lockhart and Satya-Murti (1) with interest, but also with some concern. I am sure I am wrong, and I look forward to the authors educating me on the issue, but the article seems to suggest that they believe that the diagnostic value of clinical evidence—including visual clinical evidence—exists independently of context. Definitionally it does not. Bayes’ theorem notes that the posterior probability of a diagnosis (i.e., the probability of a diagnosis given some evidence) is a function of the prior probabilities of the presence of the diagnosis regardless of the evidence, and the presence of the evidence regardless of the diagnosis. Similarly, the positive predictive value of a finding is a function of the prevalence of the disease. These prior probabilities are cohort-specific. History and context are the primary ways in which these cohorts are identified. A “positive” pregnancy test is both highly sensitive and specific for pregnancy in women of childbearing age. However, it has completely different implications in a male. The same appearance on X-ray or a histologic specimen may be suggestive of cancer in one patient and suggestive of a different diagnosis in another—depending on those prior probabilities. Moreover, as medical diagnosis is not a function of one simple application of Bayesian reasoning, but instead involves the construction of complex inferential networks, this dependence is on a large set of nonindependent prior probabilities (2). As evidence of the uselessness of history in radiographic examination, the authors cite an article that claims that history increases false-positive diagnoses in radiology (3). It really shows something a bit different. In that study, radiologists were presented with images and then provided with inaccurate prevalence data. Not surprisingly, the radiologists appropriately integrated that information into their diagnoses from a Bayesian perspective. Had that prevalence data been correct, the errors would likely not have been made. Had the prevalence data skewed the other way (e.g., the images were all sampled from patients with cancer and presented as from low-risk patients), then there would have been an increase in false negatives rather than false positives. That is not “cognitive bias.” That is Bayesian inference. Many articles not included in the authors’ review that involve correct clinical histories and compared diagnoses to ground truth seem to reveal decreased error when history and context are provided (4–14). I suppose that one person’s “cognitive bias” is another person’s “attentional processing” (13). As important, in radiology (and, by the way, in forensic pathology), knowing the clinical history is important in directing what studies to perform; ignorance of history and context results in useless expenditure of time and resources. As one author noted “. . . we need clinical data to ensure firstly that the most appropriate procedure is carried out, and secondly to avoid spending time and effort searching for findings that would be irrelevant in the clinical context. (9).” In one study of errors in emergency room radiology, inadequate history and physical examination were responsible for 6-7% of missed diagnoses, and “contributed to many other inappropriate conclusions.” (14) Similarly, the authors quote the Tahoe Study of Papanicolaou smear evaluation suggesting that interpretation was affected by knowledge of the human papilloma virus (HPV) status of the patient (15). The authors of that article correctly note that such knowledge affects the interpretation, but they explicitly do not show the effect it has with respect to clinical outcomes. The authors of this study speculate about the real-world effects in the final sentence of the article but propose it as a further work. As important, it is a study of screening by cytotechnologists, not of diagnoses by pathologists. They are not the same and should not be considered the same. Just as with radiology, studies in pathology that incorporate appropriate history associated with real specimens often (if not always) find a substantial benefit to the use of history and context (16–20). This salutary effect is found in forensic pathology as well (21–23). As one article looking at the effect of history on fine needle aspiration examination (FNA) noted (20):