Correspondence analysis in medical research.

Various applications of correspondence analysis to biomedical data are presented. The basic concepts of profile, mass and chi-squared distance are introduced in an initial simple example using data on the relationship between headache types and age. The main result of the correspondence analysis is a geometric map of this relationship showing how the relative frequencies of headache types change with age. A second example maps the association between personality types and various medical diagnostic groups, while a third example deals with categorical rating scales such as an efficacy scale for a medication or a scale of pain. A final example illustrates the more complex situation when several categorical variables are involved using test data on a collection of bacterial isolates, with the object of comparing bacterial types and understanding the inter-relationships of the different tests.