On the use of positive test strategies when diagnosing mental disorders

Background
Despite the adverse impact diagnostic errors can have, clinical interviewing and decision-making in psychiatric practice have received relatively little empirical attention. When diagnosing patients, clinicians tend to fall back on a specific (heuristic) rule of thumb, the positive test strategy, a confirmatory approach that increases the risk of confirmation bias.

Method and results
A group of 83 clinical psychologists and psychiatrists was asked to give their diagnostic hypotheses about two vignettes. We found them to self-generate significantly (i.e., p < .01; d = 1.57) more confirming than disconfirming questions to test their initial diagnostic impressions, with supervisors considering significantly more differential diagnoses than the less experienced post-grads/residents. When offered a list of 100 potentially relevant diagnostic queries, the supervisors selected fewer confirming and proportionally more disconfirming themes.

Conclusions
Our results demonstrate that irrespective of clinical experience mental-health clinicians indeed tend to use a confirmatory thinking style that contrasts with the stricter principle of falsification. More field-based research on this topic is needed, as well as studies probing whether a systematized diagnostic approach is feasible in psychiatric practice and increases diagnostic accuracy and patient satisfaction.