Spie charts, target plots, and radar plots for displaying comparative outcomes of health care

Abstract

Objective: Comparative evaluations of clinical outcomes (e.g., in-hospital mortality, complications after a surgical procedure) or health care processes involve the definition of several indicators for each study unit. Graphical displays are best suited for highlighting the main patterns in the data. The aim of this study was to compare different graphical techniques, including target plots, radar plots, and "spie" charts, for comparing the performances of different health care providers.

Study design and setting: Thirteen indicators were calculated and combined in eight composite indices for eight clinical categories of interest. The indices were displayed with target plots, radar plots, and "spie" charts.

Results: All the three techniques had an immediate interpretation and were easy to implement. However, target plots failed to highlight small differences between indicators, whereas radar plots were strongly influenced by the order in which the indicators were displayed. Both target and radar plots assumed equal weights for the indicators, and did not allow predetermined judgments on the relative importance of the indicators. "Spie" charts overcame the primary limitations of the other two techniques. Furthermore, they are well suited to summarize the overall performance of a health care provider with a single score.

Conclusion: "Spie" charts represented the best graphical tool for displaying multivariate health care data in comparative evaluations of clinical outcomes and processes of care among health care providers.