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The Biostatistics of Aging: From Gompertzian Mortality to an Index of Aging-Relatedness by Gilberto Levy, Bruce Levin

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3THE ARGUMENT AGAINST GOMPERTZIAN MORTALITY

Even if we took into account the boundaries described in Section 2.2.2 by restricting mortality data to deaths due to intrinsic causes and occurring within an age range of 10–90 years, there would remain questions about how good the fit by the Gompertz model to the data is and whether another distribution can provide a similarly good or better fit. In this vein, Economos (1982) forcefully challenged the status of the Gompertz model as the most appropriate and widely applied description of human mortality data: “it cannot be overemphasized that the inverse-sigmoid form of the survivorship curve makes it amenable to curve-fitting by a great variety of possible mathematical functions, one of which is Gompertz’s…the Gompertzian function is not a general ‘law’ of mortality, but rather one of the possible empirical models that are capable of fitting mortality kinetics. Once this is generally understood and accepted, the Gompertzian function will no longer be used as a Procrustean bed on which mortality kinetics are shortened or stretched until a straight line is magicked from the data!”1 We briefly take this view in Section 3.1 as we lay out some arguments and evidence for it; we then offer an outline of a possible resolution for it. We fully develop this resolution in Section 3.2.

3.1 DEPARTURES FROM THE GOMPERTZ MODEL

The long-standing notion of a good fit by the Gompertz model to human mortality data may have been overstated. Such overstatement ...

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