[Are experts immune to cognitive bias? Dependence of "confirmation bias" on specialist knowledge].

Previous studies on novice-expert differences in diagnostic reasoning have showed that experts are more flexible in the modification of their diagnostic assumptions. This implies that cognitive biases, for example, the confirmation bias should be reduced with increased domain knowledge. In this study, the dependency of the confirmation bias on the degree of expertise in diagnostic reasoning was investigated for a medical diagnosis task. Four groups of subjects (n = 32) with varying degrees of medical education (high- vs. low-domain knowledge) and experience (more than ten years versus less than five years) had to diagnose two typical cases. A preliminary diagnosis was provided and the subjects then had to assess several symptoms according to the existing diagnosis or to an alternative diagnosis that they could provide. High-domain knowledge experts modified their diagnostic assumptions earlier. They more often categorized symptoms that could have supported the preliminary or the alternative hypothesis as weakening the preliminary assumption. In general, high-domain knowledge experts have less of a confirmation bias than intermediates or novices.