Diagnostic suspicion bias

Knowledge of a subject’s prior exposures or personal biases may influence both the process and the outcome of diagnostic tests.

Background

Information about a group or individual coupled with suspicions or prejudices of medical staff could influence how diagnoses are made, by affecting what examinations are performed and how quickly people are investigated, which can affect rates of diagnosis. This can be termed diagnostic suspicion bias.

Example

As an example, if a group of workers in the industry find out that one of the chemicals they have been exposed to is a carcinogen, then these workers might present to a medical facility sooner, or be more likely to attend screening, than a non-exposed population.  Also, medical staff might more readily suspect these individuals than others to have cancer, because of the knowledge of their exposure to the carcinogen, and this might influence what tests are done and how quickly they are ordered.

Impact

Diagnostic test accuracy studies that include selected patients because they are more likely to have the condition based on clinical suspicion typically overestimate the accuracy of the test.  Studies that used non-consecutive inclusion of patients were associated with an overestimation of the diagnostic odds ratio by 50% compared with those that used a consecutive series of patients. 

A study of inpatient care for severe mental illness in the US found that researchers noticed that African Americans were three times (45% vs 19%) more likely to be diagnosed with schizophrenia than whites. Medical staff interviewing patients viewed African Americans as less honest about their symptoms, with less insight into their condition. These views were associated with higher diagnosis rates with diagnostic suspicion bias being responsible for some of the disparity in diagnosis rates.

Preventive steps

Prospective studies, with consecutive recruitment of patients and with uniform assessment and measurement throughout the study, can help avoid problems from diagnostic suspicion bias. Where retrospective studies are set up, care must be taken to avoid the effects of diagnostic suspicion bias, checking how diagnostic procedures take place, and if necessary adjusting for disparities.

Sources

Eack SM et al. Interviewer-perceived honesty as a mediator of racial disparities in the diagnosis of schizophrenia. Psychiatr Serv. 2012 Sep 1; 63(9):875-80.

Fox AJ & White GC. Bladder cancer in rubber workers: do screening and doctors’ awareness distort the statistics? Lancet 1976; 307 (7967): 1009-1010.

Porta M, et al editors. A dictionary of epidemiology. 6th edition. New York: Oxford University Press: 2014

Sackett DL. Bias in analytic research. J Chron Dis 1979; 32: 51-63

Schwartz, R & Blankenship, D. “Racial disparities in psychotic disorder diagnosis: A review of empirical literature.” World J Psychiatry. 2014 Dec 22; 4(4): 133–140.

Vandenbroucke JP, et al. Diagnostic suspicion and referral bias in studies of venous thromboembolism and oral contraceptive use. Eur J Contracept Reprod Health Care. 2001 Mar;6(1):56-7.

Whiting PF, et al. QUADAS-2 Steering Group. A systematic review classifies sources of bias and variation in diagnostic test accuracy studies. J Clin Epidemiol. 2013 Oct; 66(10):1093-104. Epub 2013 Aug 17.


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