Categorical Data Analysis Using The SAS® System, 2nd Edition

3.1. Introduction

The respiratory data displayed in Table 2.8 in the previous chapter are only a subset of the data collected in the clinical trial. The study included patients at two medical centers and produced the complete data shown in Table 3.1. These data comprise a set of two 2 × 2 tables.

Table 3.1. Respiratory Improvement

Center	Treatment	Yes	No	Total
1	Test	29	16	45
1	Placebo	14	31	45
Total		43	47	90
2	Test	37	8	45
2	Placebo	24	21	45
Total		61	29	90

Investigators were interested in whether there were overall differences in rates of improvement; however, they were concerned that the patient populations at the two centers were sufficiently different that center needed to be accounted for in the analysis. One strategy for examining the association between two variables ...