Volume 28 - Article 9 | Pages 259–270  

Gamma-Gompertz life expectancy at birth

By Trifon Missov

Response Letter

10 June 2021 | Response Letter

Error and typos in mathematical expressions

by Trifon Missov

In section "3. History and Related Results", I derive an expression for gamma-Gompertz remaining life expectancy e(x). The original article contains two errors I would like to correct:

1) I derived an expression for the integral from x to infinity of survivorship, but did not divide this by survival to x to get the final expression for e(x).

2) In the derivation on page 266, third (unnumbered) equation from the bottom there is a typo I seem to have overlooked - missing endpoints of the interval for the primitive - that makes the corresponding derivation somewhat irrational. In the Letter, I present the corrected original derivation, as well as a simpler alternative based on the substitution I made when deriving life expectancy at birth in the original article.

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