Schematic Effects on Probability Problem Solving

Three studies examined context effects on solving probability problems. Variants of word problems were written with cover stories which differed with respect to social or temporal schemas, while maintaining formal problem structure and solution procedure. In the first of these studies it was shown that problems depicting schemas in which randomness was inappropriate or unexpected for the social situation were solved less often than problems depicting schemas in which randomness was appropriate. Another set of two studies examined temporal and causal schemas, in which the convention is that events are considered in forward direction. Pairs of conditional probability (CP) problems were written depicting events E1 and E2, such that E1 either occurs before E2 or causes E2. Problems were defined with respect to the order of events expressed in CPs, so that P(E2|E1) represents the CP in schema-consistent, intact order by considering the occurrence of E1 before E2, while P(E1|E2) represents CP in schema-inconsistent, inverted order. Introductory statistics students had greater difficulty encoding CP for events in schema-inconsistent order than CP of events in conventional deterministic order. The differential effects of schematic context on solving probability problems identify specific conditions and sources of bias in human reasoning under uncertainty. In addition, these biases may be influential when evaluating empirical findings in a manner similar to that demonstrated in this paper experimentally, and may have implications for how social scientists are trained in research methodology.