Probability in Diagnostic Thinking

This chapter observes that diagnostic reasoning involves both informal and mathematical estimates of probability. It argues that intuitive estimates of the likelihood of disease are necessary in the early phases of the diagnostic process but notoriously inaccurate. It notes that formal calculations are not possible when the question is, What might be wrong with this person? but are much more accurate than intuition in estimating the probability that a specific disease is present. The chapter suggests that population-based calculations of the likelihood of disease may lead clinicians to play Russian roulette by proxy because individual variation and individual risk factors may alter that risk in a given patient. It refers to evidence that many clinicians are inexpert in statistical methods. The chapter describes some basic statistical processes and their place in the clinical application of test results. It discusses the necessity and challenges of managing patients whose symptoms are medically unexplained.