We developed and validated a prognostic index using age, gender, and self-reported functional status that effectively stratifies community-dwelling elders into groups at varying risk of 2-year mortality. Our index includes risk factors from each of the 3 groups of functional variables evaluated: dependence in ADL (bathing), dependence in IADL (shopping for groceries), and difficulty with additional measures of physical function (walking several blocks and pushing/pulling heavy objects). Our index was well calibrated, based on the similarity between mortality rates in the development and validation cohorts. Our index also showed good discrimination, with a c-statistic of 0.76 in the development cohort and 0.74 in the validation cohort. The discrimination of our index was comparable to prognostic indices that consider multiple domains of risk, including medical diagnoses and biochemical markers of disease.4,6,10
In the bivariable analyses, every functional variable we measured was associated with a 2-fold or greater increase in mortality. The functional variables that remained independently predictive of mortality in the final multivariable model were those that evaluated multiple areas of function simultaneously. Grocery shopping, for example, requires intact cognitive function to identify a need, get to the store, and manage money for payment, as well as intact physical functioning to ambulate, push a cart, reach for items, lift, and carry. Bathing is a similarly complex task; it requires upper and lower extremity dexterity, the ability to transfer safely, and the ability to dress and undress oneself. Bathing is typically the ADL with the highest prevalence of disability, and it is commonly the first ADL in which independence is lost.18,19
Previous studies have demonstrated the prognostic value of functional status by showing that functional impairment was independently predictive of mortality when used alongside other, more conventional predictors such as disease status.4,7
Inouye et al. developed a 3-item functional index that, when added to commonly used burden of illness scores, such as the Charlson index, substantially improved their ability to predict 90-day and 2-year mortality in hospitalized patients.5
However, our study is the first to demonstrate that simple self-reported measures of function, along with age and gender, can be used together to stratify community-dwelling elders into groups at variable risk for mortality. In particular, we identified groups at low (5%) and high (36%) risk of mortality in 2 years. According to the U.S. life tables for the year 2000, an 80-year-old has a 2-year mortality of 12%,20
which was the average mortality of our entire cohort and the mortality of our middle-risk group. According to our index, however, a fully functional 80-year-old woman has a mortality of less than half that, whereas an 80 year-old woman who is dependent in all of the functional measures of our index has a mortality that is 3 times higher than that.
We used a population-based cohort representative of community-dwelling elders in the United States. Although 95% of elders live in the community and are outpatients,19
most prognostic indices have been developed for use in hospitalized elders, who are sicker and have higher mortality rates. Many of these indices specifically attempt to identify patients at high risk of immediate death, with the goal of identifying patients in whom transition to palliative care is appropriate. In community-dwelling elders, however, short-term mortality is much lower, such that the expected mortality rate for an 80-year-old over 2 years is only 12%.20
In our study, we were able to identify a large group of extremely well elders, whose mortality rate was less than half that (5%), and a smaller group of sick elders with a mortality rate 3 times as high (36%), such that there was a 7-fold difference in mortality rates among these elders overall. There is tremendous value in identifying elders at either extreme. In our study, we identified a large group of extremely well elders, with much longer than average life expectancies. Indeed, our lowest risk group was the largest group we identified, including 46% of the development cohort and 41% of the validation cohort. Identifying elders at significantly lower risk of death than average can help health care providers appropriately target interventions, such as cancer screening tests, many of which have a lag time to benefit of 5 to 10 years.21
These extremely well elders, with greater than average life expectancies, are in the best position to benefit from preventive interventions and health care maintenance efforts, with the goals of maintaining and even improving their health. There is also, however, a great need to identify those elders who are approaching the end of their lives but not imminently at risk of death. In our study, our highest risk group, which accounted for approximately 12% of the development cohort and 14% of the validation cohort, had a mortality rate of 36%, which is lower than is seen in mortality indices developed in sicker patients. However, we sampled well, community-dwelling elders for whom a 36% mortality rate over 2 years represents a 3-fold increase over expected mortality. Identifying elders at considerably higher risk for death than average can help identify patients in whom discussions about goals of care, treatment preferences, and advance directives may be particularly appropriate. Such discussions are best held with patients long before the time of death, while patients are still competent to state their own preferences. The tremendous heterogeneity of the growing elderly population demands that we improve our ability to prognosticate so that we can provide each person with the best individualized care. Without improving prognostication strategies for elders, we will continue to make important errors of undertreatment and overtreatment.
Our study, in highlighting the prognostic impact of functional status, provides further evidence for the importance of assessing functional status. Functional status reflects the end-impact of illnesses and psychosocial factors on a given patient, and it is likely that this explains its prognostic value. The value of functional status, however, extends far beyond prognosis. Knowing a patient's function helps to provide high-quality care: functional status assessment is vital to determining a patient's long-term care needs, to providing patients with appropriate therapies, and to assessing a caregiver's needs. Functional dependency is a risk factor not only for mortality, but also for nursing home placement and elder mistreatment.10,19,22
With the investment of just a few minutes of time, one can gain rich clinical and prognostic information about a patient through assessing functional status. Yet, despite its importance and the ease of obtaining this information, physicians often fail to recognize functional disability in their patients.23
Our prognostic index provides a simple and effective means of estimating mortality that can be used in a variety of settings. It applies an easy-to-use point scoring system, and all the necessary variables can be obtained through patient interview alone. In addition to clinical uses, our index also may have important research and health policy uses, in that it could provide a simple means of risk stratifying patients to account for unmeasured differences in illness severity. For example, using our index to risk adjust for mortality in different settings may facilitate quality of care comparisons and evaluations of medical effectiveness. Our index could also be helpful in observational studies, in which subtle baseline differences in functional status are important aspects of health outcomes. In addition, using our index as a tool to account for baseline illness severity in different settings, such as Medicare HMOs, may be beneficial in setting reimbursement rates that more accurately reflect the illness severity of the population.
While a strength of our study was our use of a large sample of community-dwelling elders that is representative of the U.S. population, there are several methodological considerations that should be taken into account in evaluating the generalizability of our results. First, our sample was generally healthy, with only 13% of the development cohort being dependent in 1 or more ADL. However, approximately 60% of each cohort had difficulty with 1 or more of the additional measures of physical function, such as walking several blocks. As a result, the additional measures of physical function better differentiated outcomes than ADL dependence. In a more severely ill population, it is likely that ADL impairment would have better distinguished between patients at variable risk for death. Second, we only considered 2-year mortality for our index. It is likely that we may have found different predictors of mortality had we used a different time frame as our endpoint. Third, there are many methods of asking about functional status, and the prognostic value of functional measures may differ depending on how the measure is assessed. For example, asking about ADL and IADL difficulty instead of dependence would likely have resulted in greater levels of impairment but perhaps a smaller association with mortality. In addition, while we assessed dependence for ADLs and IADLs, we only asked about difficulty for the additional measures of physical function because walking several blocks and pushing furniture are not tasks essential for daily functioning and independent living. Finally, all of our functional data relied on patient or proxy report. While it may be the case that clinical evaluation and observation provide a more reliable measure of function, this is often less practical. A patient's gait can be tested in the office hallway, but it is not so simple to test a patient's ability to grocery shop or bathe. In addition, there is evidence that patient and proxy reports provide valid measures of function.24
Future research should assess whether performance-based or patient-reported functional measures have a better prognostic performance.
In summary, we developed and validated a prognostic index using a few simple measures of functional status, along with age and gender. Our index employs a simple point-scoring system, using measures that can be obtained by patient interview alone, without need for a medical chart or laboratory data. It effectively stratifies elders into groups at varying risks of death, and it can be used in a variety of different settings. Our findings provide further evidence of the prognostic importance of functional status, demonstrating that evaluating function has important clinical, policy, and research uses.