There are various techniques available for the principal component analysis
(PCA) of binary matrices. We illustrate some of them in this chapter by
analyzing votes on 20 issues in the 2001 US Senate, selected by Americans
for Democratic Action [Americans for Democratic Action, 2002]. It must
be emphasized that the techniques we discuss are general, because they
apply to many different types of binary matrices. They can be used equally
effectively, for example, to analyze data from choice experiments or from
tests and exams.