Heuristics and biases: Selected errors in clinical reasoning

Many clinical decisions are made in uncertainty. When the diagnosis is unce rtain, the goal is to establish a diagnosis or to treat even if the diagnos is remains unknown. If the diagnosis is known (e.g., breast cancer or prost ate cancer) but the treatment is risky and its outcome uncertain, still a c hoice must be made. In researching the psychology of clinical judgment and decision making, the major strategy is to compare observed clinical judgmen ts and decisions with the normative model established by statistical :decis ion theory. In this framework, the process of diagnosing is conceptualized as using imperfect information to revise opinions; Bayes' theorem is the fo rmal rule:for updating a diagnosis as new data are available. Treatment;dec isions should be made so as:to maximize expected value. This essay uses Bay es' theorem and concepts from decision theory to describe and explain some well-documented errors in clinical reasoning. Heuristics and biases are the cognitive factors-that produce these errors.