A new time-series methodology for estimating relationships between elderly frailty, remaining life expectancy, and ambient air quality.
BACKGROUND
Many publications estimate short-term air pollution-mortality risks, but few estimate the associated changes in life-expectancies.


OBJECTIVE
We present a new methodology for analyzing time series of health effects, in which prior frailty is assumed to precede short-term elderly nontraumatic mortality. The model is based on a subpopulation of frail individuals whose entries and exits (deaths) are functions of daily and lagged environmental conditions: ambient temperature/season, airborne particles, and ozone. This frail susceptible population is unknown; its fluctuations cannot be observed but are estimated using maximum-likelihood methods with the Kalman filter. We used an existing 14-y set of daily data to illustrate the model and then tested the assumption of prior frailty with a new generalized model that estimates the portion of the daily death count allocated to nonfrail individuals.


RESULTS
In this demonstration dataset, new entries into the high-risk pool are associated with lower ambient temperatures and higher concentrations of particulate matter and ozone. Accounting for these effects on antecedent frailty reduces this at-risk population, yielding frail life expectancies of 5-7 days. Associations between environmental factors and entries to the at-risk pool are about twice as strong as for mortality. Nonfrail elderly deaths are seen to make only small contributions.


CONCLUSIONS
This new model predicts a small short-lived frail population-at-risk that is stable over a wide range of environmental conditions. The predicted effects of pollution on new entries and deaths are robust and consistent with conventional morbidity/mortality times-series studies. We recommend model verification using other suitable datasets.
Department of Economics, University of Houston, Houston, TX, USA.
Christian J
CJ
Murray
Frederick W
FW
Lipfert
D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000633:toxicity; D000397:Air Pollution / Q000009:adverse effects*; D016330:Frail Elderly / Q000706:statistics & numerical data*; D006801:Humans; D008017:Life Expectancy; D008962:Models, Theoretical; D009026:Mortality; D010126:Ozone / Q000633:toxicity; D052638:Particulate Matter / Q000633:toxicity; D015143:Philadelphia
D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone