Strange but true: Corroboration and base rate neglect.

How do we deal with unlikely witness testimonies? Whether in legal or everyday reasoning, corroborative evidence is generally considered a strong marker of support for the reported hypothesis. However, questions remain regarding how the prior probability, or base rate, of that hypothesis interacts with corroboration. Using a Bayesian network model, we illustrate an inverse relationship between the base rate of a hypothesis, and the support provided by corroboration. More precisely, as the base rate of hypothesis becomes more unlikely (and thus there is lower expectation of corroborating testimony), each piece of confirming testimony provides a nonlinear increase in support, relative to a more commonplace hypothesis-assuming independence between witnesses. We show across 3 experiments that lay reasoners consistently fail to account for this impact of (rare) base rates in both diagnostic and intercausal reasoning, resulting in substantial underestimation in belief updating. We consider this a novel demonstration of an inverted form of base rate neglect. We highlight the implications of this work for any scenario in which one cannot assume the confirmation or disconfirmation of a reported hypothesis is uniform. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Failures to replicate a key result of the selective accessibility theory of anchoring.

Numerical anchoring effects describe the assimilative effect of a previously presented number on subsequent numerical estimates. Such effects are robust and consequential. A number of different accounts have been proposed to explain these effects. What is currently unclear is under which situations different mechanisms play more or less critical roles. An extant test from the literature is proposed as a "signature test" for the operation of selective accessibility mechanisms. Four experiments were conducted to ascertain the evidence for selective accessibility with this test, evidence which was not obtained. A fifth experiment employed a different methodology, and again failed to show evidence for selective accessibility. Subsequent discussion suggests that the robustness of anchoring effects is remarkable, but the theoretical basis for some previous tests of the selective accessibility account of anchoring is shaky, and we advise against their use in this capacity. (PsycINFO Database Record (c) 2019 APA, all rights reserved).