The discrimination of graphical elements

A model is proposed to account for how people discriminate quantities shown in pie charts and divided bar graphs (i.e. which proportion is larger, A o r B?). The incremental estimation model assumes that an observer sequential ly samples from the available perceptual features in a graph. The relative effectiveness of sampled perceptual features is represented by the spread o f probability distributions, in the manner of signal detection theory. The model's predictions were tested in two experiments. Participants took longe r with pies than divided bars and longer with non-aligned than aligned prop ortions in Experiment 1. In Experiment 2, participants took longer with div ided bars than pies when graphs were of unequal size. Generally, graphical formats producing longer response times incurred a greater time penalty whe n the difference between proportions was reduced. These results were in acc ordance with the model's predictions. Implications for graphical display de sign are discussed. Copyright (C) 2001 John Wiley & Sons, Ltd.