Causal knowledge has been shown to affect diagnostic decisions. It is unclear, however, how
causal knowledge affects diagnosis. We hypothesized that it influences intuitive reasoning
processes. More precisely, we speculated that people automatically assess the coherence
between observed symptoms and an assumed causal model of a disorder, which in turn
affects diagnostic classification. Intuitive causal reasoning was investigated in an
experimental study. Participants were asked to read clinical reports before deciding on a
diagnosis. Intuitive processing was studied by analysing reading times. It turned out that
reading times were slower when causally expected consequences of present symptoms were
missing or effects of absent causes were present. This causal incoherence effect was
predictive of participants’ later explicit diagnostic judgments. These and related findings
suggest that diagnostic judgments rely on automatic reasoning processes based on the
computation of causal coherence. Potential implications of these results for the training of
clinicians are discussed.
