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

13.2. Weighted Least Squares Methodology

To motivate the discussion of weighted least squares methodology, consider the following example. Epidemiologists investigating air pollution effects conducted a study of childhood respiratory disease (Stokes 1986). Investigators visited groups of children two times and recorded whether they were exhibiting symptoms of colds. The children were recorded as having no periods with a cold, one period with a cold, or two periods with a cold. Investigators were interested in determining whether sex or residence affected the distribution of colds. These data are displayed in Table 13.1.

Table 13.1. Colds in Children

		Periods with Colds
Sex	Residence	0	1	2	Total
Female	Rural	45	64	71	180
Female	Urban	80	104	116	300
Male	Rural