Background: This study tests the influence of different response modes (direct, after conscious and after unconscious thinking) in clinical decision making. Recently, we published a first demonstration of unconscious thought effects in this domain, specifically in the complex and error-prone task of diagnostic classification (De Vries et al., in press). The current study describes a follow-up and refinement, in three ways. First, it investigated the role of experience by including experienced clinicians. Second, it included the degree of difficulty of classifications. Third, it included a third (control) condition in which classifications were provided immediately after reading a case description.
Methods: We used two written case descriptions. Both cases represented co-morbidity, with a more familiar classification (low difficulty) and a much more unfamiliar classification (high difficulty). Participants were randomly assigned the task in two of three response modes: conscious-processing (i.e., deliberately thinking about the information in the case description), unconscious-processing (i.e., deciding after performing an unrelated distracter task), or direct responding, without any delay or intervening task. Our main dependent measure was the proportion of correct classifications.
Results: A GLM analysis revealed a significant three way interaction, see Figure 1. For classifications low in difficulty, novices performed best after conscious processing. Experienced clinicians, in contrast, performed worst after conscious processing. For classifications high in difficulty, experienced clinicians outperformed novices. Moreover, both conscious and unconscious processing resulted in better performance than immediate classification. Figure 1: Proportion of correct classifications as a function of Processing Condition, Difficulty and Experience Level. Conclusion: The occurrence of diagnostic errors in psychiatric classifications appears to be a complex function of information processing mode, level of experience and task difficulty. In case of familiar classifications, experienced diagnosticians perform best when they respond either directly, or after unconscious processing, probably due to a well-developed intuition through years of practice with similar cases. Conscious thought may make them take irrelevant information into account. Novices have not had many experiences with similar cases yet, but have recently learned explicit rules for classification tasks, which may explain why they perform best after conscious thought when a classification is relatively easy. When cases become more unfamiliar, no response is directly available in memory and further –conscious or unconscious- information processing seems to be required. De Vries et al., (in press). The unconscious thought effect in clinical decision making: An example in diagnosis. Medical Decision Making. 
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