The perception of scatterplots

Four experiments investigated the perception of correlations from scatterplots. All graphic properties, other than error variance, that have been shown to affect subjective but not objective correlation (r) were held constant. Participants in Experiment 1 ranked 21 scatterplots according to the magnitude of r. In Experiments 2 and 3, participants made yes/no judgments to indicate whether a scatterplot was high (signal) or low (noise). Values of r for signal and noise scatterplots varied across participants. Differences between correlations for signal and for noise scatterplots were constant in r in Experiment 2, and constant in r2 in Experiment 3. Standard deviations of the ranks in Experiment 1 and d' values in Experiments 2 and 3 showed that discriminability increased with the magnitude of r. In Experiment 4, faculty and graduate students in psychology and sociology made point estimates of r for single scatterplots. Estimates were negatively accelerated functions of objective correlation.