6. Based on the study description preceding Exercise 1, do you think that the likelihood ratio and Wald test resuIts will be approximately the same? Explain.

A prevalence study of predictors of surgical wo und infection in 265 hospitals throughout Australia collected data on 12,742 surgical patients (McLaws et al., Med. J. of Australia, 1988). For each patient, the following independent variables were determined: type of hospital (public or private), size of hospital (large or small), degree of contamination of surgical site (clean or contaminated), and age and sex of the patient. A logistic model was fit to this data to predict whether or not the patient developed a surgical wound infection during hospitalization. The largest model fit included all of the above variables and all possible two-way interaction terms. The abbreviated variable names and the manner in which the variables werc coded in the model are described as folIows:

Variable Abbreviation Co ding Type of hospital HT 1 = public, 0 = private Size of hospital HS 1 = large, 0 = small Degree of contamination CT 1 = contaminated, 0 = clean Age AGE continuous Sex SEX 1 = female, 0 = male