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Dual process theory (DPT) and the intertwined concepts of heuristics and biases, popularised by Kahneman's book Thinking Fast and Slow, are widely discussed models for analysing decision-making processes inside and outside medicine.1 The basic premise of DPT is that the brain has a fast, intuitive, but occasionally error-prone system (system 1) and a slower, energy-intensive but more accurate analytical system (system 2). Inexorably tied up with the DPT model is the idea that the errors made in system 1 are a result of shortcuts (heuristics) and predispositions (biases) and the hope that if we spent more time in system 2, cognitive errors could be mitigated.
Insights from this model have driven quality improvement and medical education efforts. Learning about how our brain succeeds and fails is interesting, humbling and motivating—but is it effective? My instinct has always been that it is, but as I have tried to answer key questions that my own DPT-based teaching inevitably brings up, I have become less certain.
Can I show accurate examples of system 1 or system 2 thinking?
One of the ways to bring the model to life is to provide examples, but it is difficult to find examples of pure system 1 or system 2 thinking in clinical medicine. Like others, I use the herpes zoster rash as a system 1 prototype, but then explain how a good clinician always asks a few questions and carefully inspects the rash before declaring their conclusion. The stock system 2 example is a mathematical analysis of pretest and post-test probability of pulmonary embolus, but I eventually disclose that emotional dimensions like regret also influence the decision to order a CT angiogram. Analysis of every case shows that some aspects of the clinical reasoning process (eg, hypothesis generation) are intuitive, while other phases (eg, hypothesis verification) are more analytical. One quickly finds himself/herself telling …
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