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Life expectancy estimation with breast cancer: bias of the declining exponential function and an alternative to its
R R Holland1, C A Ellis, B M Geller
1Office of Health Promotion Research, Burlington, Vermont 05401-3444, USA. rholland@sover.net
Background:
Life expectancy gain (LEG) is an outcome measure commonly estimated with a declining exponential function in a Markov model. The accuracy of such estimates has not been objectively evaluated.
Purpose:
To compare LEGs from declining exponential function estimates with those calculated from population data, using published screening mammography studies as examples.
Method:
SEER-based population data are used to compare LEG calculation with declining exponential function estimation and empiric population data in a new model, the "nested" Markov.
Results:
Analyses of the LEG of mammographic screening based on the declining exponential function significantly overestimate LEGs for younger women and underestimate them for older women. Because of offsetting errors, all-age analyses paradoxically appear accurate.
Conclusion:
Declining exponential function estimates of LEGs for chronic diseases with low mortality rates and long time horizons are liable to significant bias, especially with limited age cohorts.
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