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Related Experiment Videos

Judgments of proportions.

C A Varey1, B A Mellers, M H Birnbaum

  • 1University of California, Berkeley 94720.

Journal of Experimental Psychology. Human Perception and Performance
|August 1, 1990
PubMed
Summary

People often misjudge proportions, overestimating small amounts and underestimating large ones. This study shows how these frequency estimation errors occur, even when using correct mathematical operations.

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Area of Science:

  • Cognitive Psychology
  • Human Perception
  • Judgment and Decision Making

Background:

  • Estimating relative frequency is a fundamental cognitive process.
  • Previous research suggests systematic biases in human judgment.

Purpose of the Study:

  • To investigate the underlying cognitive processes of relative frequency estimation.
  • To examine how different instructed operations (percentage, ratio, difference) affect proportion judgments.
  • To test the predictions of range-frequency theory on these judgments.

Main Methods:

  • Participants performed four distinct tasks involving visual stimuli (squares with black and white dots).
  • Tasks required judgments of percentages, ratios, and differences between dot quantities.
  • Stimuli varied in actual proportion distributions to test range-frequency theory.

Main Results:

  • Participants consistently used the same underlying scale values across different instructed operations.
  • A significant bias was observed: overestimation of small proportions and underestimation of large proportions.
  • The degree of these biases was influenced by the distribution of actual proportions, aligning with range-frequency theory predictions.

Conclusions:

  • Proportion judgments are not always accurate and should be interpreted cautiously.
  • Cognitive biases in frequency estimation persist even when correct mathematical operations are applied.
  • Range-frequency theory provides a useful framework for understanding systematic errors in proportion and probability judgments.

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