Patient
Patient variables included age, gender, primary medical
diagnoses, marital status and comorbidities. ‘Comorbidities’
were defined as a patient’s other illnesses
on admission but not the principal reason for admission.
Comorbidities were extracted from a list of secondary
diagnoses, using Elixhauser et al. (1998) 30
comorbidities identification method and the ICD-
9-CM codes identified by Agabiti et al. (2007) as comorbidities
specific to the patients undergoing hip
replacements. Because of high variability in the identified
comorbidities for the patients in this study, the
number of comorbidities – instead of each individual’s
specific comorbidities – was entered for the analyses.