Judgments of Proportion with Graphs: Object-based Advantages

This study investigated whether a stacked bar’s vertical arrangement or single-object properties underlie its accuracy for proportion judgments. We hypothesized that observers would be less accurate when stacked bars were separated than when they formed a single object, according to the object-based theory of attention (Duncan, 1984). Thirty participants judged proportions with three different graph types: bars, stacked bars, and staggered stacked bars. Stacked bars produced smaller error than staggered stacked bars, while bars produced the greatest error. The results show an object-based advantage for stacked bars, but a vertical arrangement advantage for staggered stacked bars over bars was also evident.