Probabilistic judgment on a coarser scale

We hypothesize that when assessing the likelihood of uncertain events, statistically unsophisticated people utilize a coarse internal scale that only has a limited number of categories. The present paper reports two experiments on probabilistic judgment to test this hypothesis. In Experiment 1, participants estimated event probabilities freely and we found that their responses were highly clustered despite the even and nearly continuous distribution of the target probabilities. In Experiment 2, participants made forced comparisons using two different external response scales (coarser versus finer). We found that their performance did not measure up to the requirement of the finer scale. These findings indicate that besides the systematic biases, a certain portion of human errors in probabilistic judgment may be due to the low resolution of the internal representations.