Demographic and clinical information are displayed in Table 1. A total of 136 subjects died during the period of analysis (October 1998 to October 2002; mean observation days: 1128 [SD=235] days). Their average age at the time of death was 83.1 (SD=7.5) years and the average time to death was 699.5 (SD=324.5) days after initial evaluation. The deceased included one participant with no cognitive diagnosis, 24 participants with mild cognitive impairment, and 111 participants with probable dementia. The cause of death based on the knowledgebale informant’s report and Medicare records were as following: cardiovascular or cerebrovascular events (40.1%), cancer (19.3%), infection (10.4%), physical complications of dementia (e.g., inability to swallow) (6%), kidney failure (3%), and unspecified causes (20%).
Kaplan-Meier survival estimates indicated higher mortality rates for those with more severe levels of cognitive impairment. Log rank test verified that the trend in mortality rates across the risk groups (no cognitive diorder, mild cognitive impairment, mild dementia, moderate dementia, and severe dementia) was statistically significant (chi2=30.87, df=4, p=0.0001). In the Cox hazard proportional model analysis that included all of the variables above, age (hazard ratio=1.05, 95% confidence interval [1.02, 1.08], p=0.001), gender (0.44 [0.27, 0.73], p=0.004), and MMSE (0.95, [0.92, 0.97], p=0.001) or level of cognition (1.512, [1.250, 1.852], p=0.001) were statistically significant. In contrast, measures of health and disease (physical health rating by the knowledgeable informant, presence of heart disease, stroke, diabetes, chronic obstructive pulmonary disease, asthma, and cancer) were not significant (p>0.05) as covariates. Cox regression survival plot for mortality by levels of cognitive impairment (Figure 1) indicates that cognitive diagnosis is significantly associated with mortality among the participants.