A Model for Studying Display Methods of Statistical Graphics

Abstract

A method of statistical graphics consists of two parts: a selection of statistical information to be displayed and a selection of a visual display method to encode the information. Some display methods lead to efficient, accurate visual decoding of encoded information, and others lead to inefficient, inaccurate decoding. It is only through rigorous studies of visual decoding that informed judgments can be made about how to choose display methods. A model has been developed to provide a framework for the study of visual decoding. The model consists of three parts: (1) a two-way classification of information on displays—quantitative-scale, quantitative-physical, categorical-scale, and categorical-physical; (2) a division of the visual processing of graphical displays into pattern perception and table look-up; (3) a specification of visual operations that are employed to carry out pattern perception and table look-up. Display methods are assessed by studying the visual operations to which they lead. Studies use the theory and experimental technique of various areas of vision research including psychophysics, cognitive psychology, and computational vision. This process is illustrated by studies of three display methods: visual reference grids for graphs with juxtaposed panels and common scales, encoding a categorical variable on a scatterplot by the type of plotting symbol, and choosing the aspect ratio of a factor-response graph.