Subjective significance judgments

Observers were presented with random spatial distributions of dots, inside and outside a small highlighted region, and required to judge to what extent their density was significantly different. Experiment 1 examined whether the absolute density of the target area affects significance judgments, and evaluated the size of this bias compared to that of the normative statistical significance, using regression analysis; the regression weight of statistical significance was about four times larger than the absolute target value. Experiment 2 investigated the effect of increasing the size of the cells, which dilutes the dots in a larger area without affecting the statistical task. This factor produced a small residual effect, suggesting the involvement of a perceptual mechanism in statistical processing. The third experiment found that statistically explicit instructions both increases the influence of the statistical information and reduces the absolute density bias found in Experiment 1.