Office of Health Promotion Research
Holland RR, Ellis CA, Geller BM, Plante DA, Secker-Walker RH. Life expectancy estimation with breast cancer: bias of the declining exponential function and an alternative to its use. Med Decis Making. 1999 Oct-Dec;19(4):385-93. [Comment in: Med Decis Making. 1999 Oct-Dec;19(4):503-4.]
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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