We developed and validated a prognostic index that can be used to predict 5-year mortality for community-dwelling US adults. Our index shows excellent calibration as demonstrated by similar mortality rates in the development and validation cohorts and strong discrimination as demonstrated by increasing risk of mortality by point score. Specifically, our index can be used to address questions related to life expectancy when using NHIS or related datasets such as MEPS. After validation in the clinical setting, the index may also be used by clinicians to estimate patient’s 5-year mortality. This is important since increasingly clinicians are being asked to make decisions on disease prevention and treatment based on patient life expectancy.
We and others have previously performed studies using NHIS to examine receipt of preventive health measures (e.g., cancer screening, exercise counseling, immunizations) among older adults using health status as a proxy for life expectancy.4–11
We did this because there was no validated index of mortality available for use with NHIS at that time. The index developed in this paper provides opportunity for health services researchers to examine receipt of screening and other health services by life expectancy among US adults using NHIS.
One of the potential clinical applications of our index may be in helping clinicians decide which women aged 80 and older to screen with mammography. There are no data from clinical trials to help guide this decision, and guidelines recommend that clinicians consider patient life expectancy.19
Based on life expectancy tables, the average life expectancy of a woman aged 80 is 9.8 years 25
; however, there is significant variation among individual women. Several studies have shown that clinicians are poor predictors of patient life expectancy 26,27
and that prediction models can help improve these estimates.28
According to our index, a woman aged 80 with no other risk factors would score 5 points and would have only an 8% probability of 5-year mortality; mammography screening would likely be appropriate for this woman. Meanwhile, an 80-year-old female who is a former smoker with COPD and diabetes, who needs help with shopping, has difficulty walking a quarter mile, and perceives herself to be in fair health, would score 17 points. This hypothetical woman would have a more than 50% probability of dying within 5 years, and it would likely be appropriate to counsel her about stopping screening. Other examples where our index might be useful may be in helping clinicians decide which of their older patients may benefit from tight glycemic control, from joint replacement surgery, or repair of an abdominal aortic aneurysm, and which are unlikely to benefit due to shortened life expectancy.2
As previously mentioned, Lee et al. developed a tool to be used by researchers and/or clinicians to estimate individuals’ 4-year mortality.18
Like our index, the Lee et al. index includes age, sex, BMI, history of diabetes and cancer, and difficulty with walking as risk factors. The Lee index also includes lung disease, smoking status, and difficulty managing money, similar to items included in our index, but worded differently. Three factors in the Lee index were not included in our index: difficulty with pulling and pushing, difficulty with bathing, and history of congestive heart failure. The former two were assessed in NHIS, but did not make it into our final model, whereas congestive heart failure is not assessed specifically in NHIS. Our index additionally includes perceived health and hospitalizations in the past year, which are important independent predictors of mortality. 29,30
Besides its applicability to NHIS, a large nationally representative survey of US adults administered annually, our index predicts 5-year mortality, which may be more clinically useful, and was developed using survival methods rather than logistic regression.
Our index has notable limitations. First, it was developed for community-dwelling adults who can provide self-report, and therefore cannot be generalized to nursing home residents or those with dementia. However, another mortality index has been developed specifically for this group.12
Second, follow-up is currently available only through 31 December 2002. Future studies can evaluate the index prospectively as additional years of NHIS mortality data become available. Finally, the index has yet to be validated in a clinical setting.
In summary, we have developed a mortality index to predict 5-year mortality among community-dwelling older adults. This index may be valuable to researchers using NHIS or MEPS to address important health service questions. Importantly, it may also be useful to clinicians who would like to target certain clinical services to older adults based on life expectancy.