When people are asked to estimate the probability of an event occurring, they sometimes make different subjective probability (SP) judgments for different descriptions of the same event. This implies the evidence or support recruited to make SPs is based on the descriptions of the events (hypotheses) instead of the events themselves, as captured by Tversky and Koehler's (1994) support theory. However, is the support assigned to a hypothesis invariant, as support theory assumes? Here, across two studies where participants were asked to estimate the probability that an event would occur, we show that the support people recruit about the target hypothesis also depends on the other hypotheses under consideration. The first study shows that the presence of a distractor---a hypothesis objectively dominated by the target hypothesis---boosts the SP assigned to the target hypothesis. The second study shows that the presence of a resembler---a hypothesis that is objectively similar to the target hypothesis---detracts more from the SP assigned to the target hypothesis than the competing hypothesis. These context effects invalidate the regularity and the strong independence assumptions of support theory and more generally suggest a similar process that drives the construction of preference also underlies belief.
The role of ANS acuity and numeracy for the calibration and the coherence of subjective probability judgments
