Academic journal article Human Factors

Information Structure and the Relative Efficacy of Tables and Graphs

Academic journal article Human Factors

Information Structure and the Relative Efficacy of Tables and Graphs

Article excerpt

Users and system designers often prefer to display information with graphs rather than with tables. However, empirical studies that compared task performance with the two display types frequently revealed either an advantage of tables over graphs or no differences between the displays. This apparent contradiction may result from previous studies in which the importance of the structure that usually exists in displayed information is overlooked. We predict that graphic displays will have an advantage over tables when the displayed information has structure and when this structure is relevant for the task. These conditions generally exist in the actual use of information displays, but have seldom been assessed in experiments. In the present study participants in an experiment performed an information extraction task and a prediction task with unstructured or structured data and with different levels of prior information about the structure. The results showed that the information structure and prior knowledge a bout the existence of structure affected the advantage of graphic displays over tables when task performance depended on the use of structure. Existing approaches to the study of displays were analyzed in view of these findings. Actual or potential applications of this research include the development of better displays for process control and decision support and better operator training programs.

INTRODUCTION

Information Structure and the Relative Efficacy of Tables and Graphs

Computerized information technologies are designed to support complex decision making in modem work environments. This decision support is vital for many fields, whether for the operator in the control room of a plant, the business executive assessing financial and operational information, or the scientist reviewing the results of a study. However, although computers facilitate the collection, storage, and processing of data, decisions still depend largely on a person's ability to obtain relevant information from displays. Information that is difficult to extract from the display may be ignored or devalued, whereas information that is particularly salient is likely to have a strong effect on decisions (Jarvenpaa, 1990). It is therefore important to determine which information is most easily available in different displays. Because one can broadly distinguish between graphic and alphanumeric (i.e., tabular) displays, the salience and availability of different types of information in these two display types sh ould be examined first.

Jarvenpaa and Dickson (1988) expressed a commonly held view about the relative efficacy of tables and graphs: Vendors and graphics proponents have generally advocated the use of graphics over tables for the following elementary tasks: (1) summarizing data, (2) showing trends and relationships over time, (3) comparing data points and relationships of variables, (4) detecting deviations and differences in data.[ldots] We are unaware of any claims having been made, however, to suggest that graphics are more effective for (5) point reading. (P. 767)

This claim resembles Washburne's (1927) statement that tables are best for the recall of specific amounts, pictographs for simple comparisons, bar graphs for comparisons, and line graphs for the recall of trends. Although these recommendations correspond with widely held beliefs, an analysis of the empirical studies that were conducted over the last 70 years does not provide unequivocal support for such generalizations. Furthermore, a reanalysis of Washburne's original data (Meyer, 1997) showed that three of his four conclusions are not at all or only partly supported by his own findings.

Other studies comparing graphic and tabular displays reveal the same inconclusive picture. For instance DeSanctis (1984) quoted 7 studies showing an advantage of graphs, 12 studies showing an advantage of tables, and 10 studies showing no difference between the displays. …

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