Differences in the weighting and choice of evidence for plausible versus implausible causes.

Individuals have difficulty changing their causal beliefs in light of contradictory evidence. We hypothesized that this difficulty arises because people facing implausible causes give greater consideration to causal alternatives, which, because of their use of a positive test strategy, leads to differential weighting of contingency evidence. Across 4 experiments, participants learned about plausible or implausible causes of outcomes. Additionally, we assessed the effects of participants' ability to think of alternative causes of the outcomes. Participants either saw complete frequency information (Experiments 1 and 2) or chose what information to see (Experiments 3 and 4). Consistent with the positive test account, participants given implausible causes were more likely to inquire about the occurrence of the outcome in the absence of the cause (Experiments 3 and 4) than those given plausible causes. Furthermore, they gave less weight to Cells A and B in a 2 × 2 contingency table and gave either equal or less weight to Cells C and D (Experiments 1 and 2). These effects were inconsistently modified by participants' ability to consider alternative causes of the outcome. The total of the observed effects are not predicted by either dominant models of normative causal inference or by the particular positive test account proposed here, but they may be commensurate with a more broadly construed positive test account.