CHAPTER 11
CATEGORICAL DATA: ANALYSIS OF
TWO-WAY FREQUENCY TABLES
In Chapter 10 we discussed the analysis of categorical or nominal data using pro-
portions. In this chapter the analysis is presented for categorical or nominal data that
have been summarized in the form of a two-way frequency table. By a two-way table
we mean a table in which counts are displayed in rows and columns. The analyses
presented here are widely used in biomedical studies. They are relatively simple to
do and are available in many statistical programs. Because they are easy to interpret,
they are sometimes used by researchers to divide ordinal data or even interval data
into groups.
This chapter is divided into five main sections. In Section 11.1 we describe dif-
ferent types of two-way tables and how different study designs lead to different types
of tables. In Section 11.2 we describe two commonly used descriptive measures
that can be calculated from frequency tables: relative risk and odds ratio. In Sec-
tion 11.3 we describe use of chi-square test for frequency tables with two rows and
two columns. Chi-square analysis of larger tables (more row or columns or both) is
given in Section 11.4. Section 1 1.5 concludes with some brief remarks.Basic Statistics: A Primer for the Biomedical Sciences, Fourth Edition.
By Olive Jean Dunn and Virginia A. Clark
Copyright @ 2009 John Wiley & Sons, Inc.141