Confirmatory information seeking is robust in psychologists' diagnostic reasoning.

Objective: Across two experiments, we examined three cognitive biases (order effects, context effects, confirmatory bias) in licensed psychologists' diagnostic reasoning.

Hypotheses: Our main prediction was that psychologist-participants would seek confirming versus disconfirming information after forming an initial diagnostic hypothesis, even given multiple opportunities to seek new information in the same case. We also expected that individual differences would affect diagnostic reasoning, such that psychologists with lower (vs. higher) cognitive reflection tendencies and larger (vs. smaller) bias blind spots would be more likely to demonstrate confirmatory bias.

Method: In Study 1, we recruited 149 licensed psychologists (M = 18 years of experience; 44% women; 71% White) and exposed them to one of four randomly assigned vignettes that varied order effects (one set of symptoms in reversed orders) and context effects (court referral vs. employer referral). They rank ordered a list of four possible initial diagnostic hypotheses and received a piped follow-up choice of which of two pieces of information (confirmatory or disconfirmatory) they wanted to test their initial hypothesis. Study 2 (n = 131; M = 21 years of experience; 53% men; 68% White) replicated and extended Study 1, following the same procedure except offering three sequential choice opportunities.

Results: Both studies found robust confirmatory information seeking: 92% sought confirmatory information in Study 1, and confirmation persisted across three opportunities in Study 2 (90%, 84%, 77%), although it lowered with each opportunity (generalized logistic mixed regression model), F(2, 378) = 3.85, p = .02, η_p² = .02.

Conclusion: These findings expand a growing body of research on bias in expert judgment. Specifically, psychologists may engage in robust confirmation bias in the process of forming diagnoses. Although further research is needed on bias and its impact on accuracy, psychologists may need to take steps to reduce confirmatory reasoning processes, such as documenting evidence for and against each decision element. (PsycInfo Database Record (c) 2024 APA, all rights reserved).