A Study to Evaluate Strategies for Teaching Effective Use of Diagnostic Tests

Research has shown that expert diagnosticians use a two-step process to confirm a diagnosis: hypothesis generation to generate diagnostic possibilities, followed by hypothesis verification to confirm the most likely diagnostic possibility.3-5 The first step appears to be non-analytical, related to pattern recognition. The second step could be calculated using analytical reasoning, however, physicians rarely make an overt calculation of conditional probabilities. Instead, experienced clinicians typically use an implicit habit or heuristic called "anchoring and adjusting" to incorporate diagnostic testing information into their thinking.6,7 Cognitive psychologists have postulated that anchoring and adjusting provides a way that probability estimates can be updated based on additional new evidence. Most of the discussion in the literature focuses on how this heuristic can lead to biased thinking because of base-rate neglect or anchoring.6 Very little discussion is on how this heuristic could be improved to yield more accurate probability estimates and whether proper use of the heuristic could be taught.

The degree to which a diagnostic test should lead to an adjustment of a probability estimate depends on the operating characteristics of a test, that is, the sensitivity and specificity. Likelihood ratios, once understood, are easier to incorporate into one's thinking, and thus could be used to calibrate the anchoring and adjusting heuristic.7

In this randomized trial, we tested whether explicit conceptual instruction on Bayesian reasoning and likelihood ratios would improve Bayesian updating, compared with a second intervention where we provided multiple (27) examples of clinical problem solving. The third arm provided minimal teaching about diagnosis, but no explicit teaching or examples.

Inclusion criteria

• Medical Student at McMaster University or Eastern Virginia Medical School
• Completed 18 months of coursework