THE EFFECTS OF INFORMATION CHARACTERISTICS ON PROBABILISTIC JUDGMENT

TAE-OK WOO, Purdue University

Abstract

The present study investigated the effects of prior probability, mode of presenting information, and information diagnosticity level on probabilistic judgments in two different decision contexts within the framework of Bayes' Theorem of probabilistic inference. In one context, subjects, playing the role of a surgeon, estimated the probability that a patient had developed lung cancer. In the other context, subjects estimated the probability that an area under investigation contained oil fields. During the initial period, subjects were informed of the prior probability. In each context, three binary and symmetrical information sources with varying degree of diagnosticity were presented in sequence. Upon receiving each item of information, subjects indicated the amount of revision they would make in their subjective probability estimates. The mode of presenting information was manipulated by presenting the information with a base unit of 10, 100, or 1,000. In Experiment 1, these base units were presented without specific reference to either sample sizes or ratios. In Experiment 2 and Experiment 3, these bases referred to ratios and sample sizes, respectively. The major findings were: (i) High prior probability produced greater conservatism than low prior probability, which seemed to be due, in part, to a ceiling effect. (ii) The information presented in terms of large base units tended to be perceived as providing stronger evidence than those presented with smaller bases, but only when diagnosticity was low. This interaction was observed only in Experiment 1. Taken together, the results from the three experiments suggest that differential cognitive processes invoked by the different presentation modes were responsible for the observed effect. (iii) Given the same amount of evidence, subjects' estimates of the probability that a patient had lung cancer were significantly higher than their estimates in the petroleum context. The effect of decision context were likely due to "availability heuristics." (iv) All items of information were generally under-processed, but this conservatism was more pronounced for highly diagnostic information.

Degree

Ph.D.

Subject Area

Educational psychology

COinS