## Judgments of proportions (1990)

Venue: | Journal of Experimental Psychology: Human Perception & Performance |

Citations: | 15 - 2 self |

### BibTeX

@ARTICLE{Varey90judgmentsof,

author = {Carol A. Varey and Barbara A. Mellers and Michael H. Birnbaum},

title = {Judgments of proportions},

journal = {Journal of Experimental Psychology: Human Perception & Performance},

year = {1990},

pages = {613--625}

}

### Years of Citing Articles

### OpenURL

### Abstract

This study investigated the processes that underlie estimates of relative frequency. Ss performed 4 tasks using the same stimuli (squares containing black and white dots); they judged "percentages" of white dots, "percentages " of black dots, "ratios " of black dots to white dots, and "differences " between the number of black and white dots. Results were consistent with the theory that Ss used the instructed operations with the same scale values in all tasks. Despite the use of the correct operation, Ss consistently overestimated small proportions and underestimated large proportions. Variations in the distributions of actual proportions affected the extent to which Ss overestimated small proportions and underestimated large proportions in the direction predicted by range-frequency theory. Results suggest that proportion judgments, and by analogy probability judgments, should not be taken at face value. Many of our real-world decisions are based on subjective probabilities. Whether we bring an umbrella to work depends on our estimate of the chance of rain; whether we buy a lottery ticket depends, in part, on our estimate of the probability of winning; whether we support nuclear power is influenced by our beliefs about the likelihood of disastrous accidents. Subjective probabilities arise from a complex mixture of our perceptions, memories, and reasoning processes. For example, to estimate the probability of rain, we might take into consideration such information as the appearance of the sky, our knowledge of past weather conditions in the area, recent weather reports, and our opinions of the weather forecasters. How such information is retrieved from memory, evaluated, and combined to form an estimate of subjective probability has been the focus of much research (e.g., Birnbaum, 1983;