Jeff Zacks and Barbara Tversky
Interpretations of graphic displays of information seem to be rooted in principles of cognitive naturalness and information processing rather than arbitrary correspondences. Both of these considerations predict that people should more readily associate bars with discrete information because bars are discrete entities and facilitate point estimates. Similarly, people should more readily associate lines with trends because lines connect discrete entities and directly represent slope. In two experiments, viewers tended to describe bar graphs in terms of discrete comparisons between individual data points, while they tended to describe line graphs in terms of continuous trends. In a third experiment, participants sketched graphic displays to illustrate verbal descriptions of data; they tended to use bar graphs to convey discrete comparisons, and line graphs to convey trends. The strength of the bar/line convention seems to depend on the communicative situation as well as the perceptual and conceptual properties of the graphic displays.