Deceased patients were identified through matching patient records with the Social Security Death Index (SSDI) either by their social security numbers or by their names with confirmed date of birth. The SSDI is a national computerized database that records death dates and locations that have been reported to the organization. Records were extracted from SSDI from 1994 through December 31, 2004; patients were thus potentially followed for mortality for between four and 10 years after their index admission. In addition, the death certificates were collected from the Maryland Division of Vital Records to determine the immediate cause and contributing causes of death. Death certificates were available for all decedents in this study.
