A Componential Model of Human Interaction with Graphs. V: Using Pie Graphs to Make Comparisons
Douglas J. Gillan · Proceedings of the Human Factors and Ergonomics Society Annual Meeting · 2000
Research and models of graph reading suggest that the reader's task is an important determinant of the perceptual and cognitive processing components that the reader uses. When people read a pie graph to determine the proportional size of a segment, they apply three processing components: selecting the appropriate mental anchor to which to compare the segment (25%, 50%, or 75%), mentally aligning the anchor to the angular position of the segment around the pie, and mentally adjusting the anchor to match the pie segment size. When a pie graph reader faces a different task, e.g., estimating the ratio of two segments or the difference between two segments, does she use the same processing components to estimate the proportions of A and of B (and then divide one estimate into the other) or does she use a more direct method of mentally aligning the two segments to be compared, then mentally overlaying one on the other (for a ratio) or estimating the spatial difference between the pie segments (for a difference). Two experiments supported the Direct models over the Proportion-based models. The component processes of the Direct models suggest that pie graph designs that eliminated the angular difference between segments being compared should improve performance.