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Testing the harvesting hypothesis by time-domain regression analysis. I: baseline analysis
Karen Fung1, Daniel Krewski, Rick Burnett
1Department of Mathematics and Statistics, University of Windsor, Windsor, Ontario, Canada.
Journal of Toxicology and Environmental Health. Part A
|July 19, 2005
Summary
Air pollution may directly increase mortality or shorten the lives of frail individuals. This study uses simulations to analyze the "harvesting" hypothesis, suggesting pollution impacts the frail population.
Area of Science:
- Environmental Health
- Epidemiology
- Biostatistics
Background:
- The link between air pollution and daily mortality is established, but underlying mechanisms remain unclear.
- A key debate questions if air pollution causes new deaths or accelerates mortality in vulnerable groups (the
Purpose of the Study:
- To investigate the
Main Methods:
- Simulations using a two-compartment population model (healthy and frail subpopulations).
- Time-domain regression analysis (Dominici et al., 2003a) to identify harvesting patterns.
- Modeling air pollution's two-step effect: transition to frail pool, then mortality.
Main Results:
- In a pure harvesting model, short air pollution episodes (<2 days) correlate with mortality if the frail pool residence time is brief.
- If pollution affects both entry and exit from the frail pool equally, log relative risk is consistent across time scales.
- Pollution disproportionately affecting the frail pool amplifies effects at shorter time scales.
Conclusions:
- Simulation results offer insights into the