Exploring contingency tables with correspondence analysis

An algorithm for correspondence analysis is described and implemented in SAS/IML (SAS Institute, 1985a). The technique is shown, through the analysis of several biological examples, to supplement the log-linear models approach to the analysis of contingency tables, both in the model identification and model interpretation stages of analysis. A simple two-way contingency table of tumor data is analyzed using correspondence analysis. This example emphasises the relationships between the parameters of the log-linear model for the table and the graphical correspondence analysis results. The technqiue is also applied to a three-way table of survey data concerning ulcer patients to demonstrate applications of simple correspondence analysis to higher dimensional tables with fixed margins. Finally, the diets and foraging behaviors of birds of the Hubbard Brook Forest are each analyzed and then a simultaneous display of the two separate but related tables is constructed to highlight relationships between the tables.