The enhancement effect in probability judgment

Abstract

Research has shown that the judged probability of an event depends on the specificity with which the focal and alternative hypotheses are described. In particular, unpacking the components of the focal hypothesis generally increases the judged probability of the focal hypothesis, while unpacking the components of the alternative hypothesis decreases the judged probability of the focal hypothesis. As a consequence, the judged probability of the union of disjoint events is generally less than the sum of their judged probabilities. This article shows that the total judged probability of a set of mutually exclusive and exhaustive hypotheses increases with the degree to which the evidence is compatible with these hypotheses. This phenomenon, which we refer to as the enhancement effect, is consistent with a descriptive account of subjective probability called support theory. © 1997 John Wiley & Sons, Ltd.

Coherence of probability judgments from uncertain evidence: Does ACH help?

“…This is because all cases in the present experiment had total evidential support exceeding unity, whereas total support was manipulated to be either high or low in the aforementioned studies. Although our finding of subadditivity is inconsistent with the formal binary complementarity axiom of support theory, the notion that subadditivity will increase with support is in fact central to support theory and referred to as the enhancement effect (Koehler, Brenner, & Tversky, 1997).…”

Probability judgment in three-category classification learning.

“…The value of T varied substantially and systematically from one symptom pattern to the next. Increased cue conflict (but not cue frequency) was associated with enhanced subadditivity: The greater the number of flu strains implicated by symptoms present in the symptom pattern, the greater the value of T. This result supports the findings of previous research (Koehler et al, 1997;Peterson & Pitz, 1988) using a much different task in which judgments are based not on general knowledge but rather on knowledge acquired during the course of the experiment.…”

Myopic Social Prediction and the Solo Comparison Effect.

“…Our data are consistent with an extension of support theory that Koehler et al (1997) called the "enhancement effect": the tendency for the total judged probability of a set of mutually exclusive and exhaustive probabilities to increase with the degree to which the evidence is compatible with the hypotheses. High performance on the quiz is compatible with winning, and participants in Experiment 4 judged the summed probability that protagonist and opponent would win as more probable in the simple competition (110%) than in the difficult competition (95%).…”