Late-life mortality plateau

In gerontology, late-life mortality deceleration is the phenomenon of hazard rate increasing at a decreasing rate in late life – rather than increasing exponentially as in the Gompertz law – and in some cases plateauing (asymptoting) at a constant rate. Graphically, on a log-linear semi-log plot (linear in the x-axis of age, logarithmic in the y-axis of hazard rate), an exponential function becomes linear, and the Gompertz law amounts to the hazard rate increasing linearly with age. Late-life mortality deceleration corresponds to hazard rate increasing more slowly than linearly (on a log-linear graph), instead curving and possibly plateauing.

Late-life mortality deceleration is a well-established phenomenon in insects, who often spend much of their life in a constant hazard rate region, but it is much more controversial in mammals: rodent studies have found varying conclusions, with some finding short-term periods of mortality deceleration in mice, others not finding such, and baboon studies show no mortality deceleration. An analogous deceleration occurs in failure rate of manufactured products; this analogy is elaborated in the reliability theory of aging and longevity.

Late-life mortality deceleration was first proposed as occurring in human aging, in (Gompertz 1825) (which also introduced the Gompertz law), and observed as occurring in humans in (Greenwood & Irwin 1939), and has since become one of the pillars of the biodemography of human longevity – see history; here "late life" is typically "after 85 years of age". However, a recent paper, (Gavrilov & Gavrilova 2011), concludes that mortality deceleration is negligible up to the age of 106 in the population studied (beyond this point, reliable data were unavailable) and that the Gompertz law is a good fit, with previous observations of deceleration being spurious, with various causes, including bad data and methodological problems – see criticism.

The primary reference for this article is (Gavrilov & Gavrilova 2011), which provides a detailed historical overview and discussion, together with current criticism.

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