Topic
Late-life mortality deceleration
The disputed hypothesis that mortality risk stops rising and levels off at very advanced ages.
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Background
Selected excerpts from Wikipedia. This is general background, not Angle's reporting, and it may have changed since the stories above were published.
In gerontology, late-life mortality deceleration is the disputed theory that hazard rate increases at a decreasing rate in late life rather than increasing exponentially as in the Gompertz law.
Late-life mortality deceleration is a well-established phenomenon in insects, which often spend much of their lives 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. Baboon studies show no mortality deceleration.
An analogous deceleration occurs in the failure rate of manufactured products; this analogy is elaborated in the reliability theory of aging and longevity.
History
A brief historical review is given in Gavrilov & Gavrilova (2011, 2. Mortality at Advanced Ages: A Historical Review (pp. 433–435)); a detailed survey is given in Olshansky (1998).
Late-life mortality deceleration was first proposed as occurring in human aging, in Gompertz (1825), which also introduced the Gompertz law. It was observed and quantified in Greenwood & Irwin (1939), and reproduced in many later studies. Greenwood and Irwin wrote:
Following these studies, late-life mortality deceleration became one of the pillars of the theory of biodemography of human longevity, and models have incorporated it. It has been criticized at times, and recently has been very seriously criticized; see below.
Criticism
Statistical studies of extreme longevity are difficult for a number of factors. Firstly, because few people live to very old ages, a very large population is required for such studies, ideally all born and living in similar conditions (same country, same birth year). In small countries, a single birth year cohort is insufficiently numerous for statistics, and thus multiple years are often used. Secondly, due to the great ages, accurate records of persons living over 100 years require records dating from the late 19th or early 20th century, when such record-keeping was often not high-quality; further, there is a tendency to exaggerate one's age, which distorts data. Thirdly, granularity is an issue – ideally exact day of birth and death would be used; using only year of birth and death introduces granularity, which adds bias (as discussed below).
Gavrilov & Gavrilova (2011) examined single birth-year cohorts from the United States Death Master File, using the method of extinct generations, and found that the effect disappeared if various distorting factors were removed. Specifically, they conclude 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, discussed below.
Given that mortality deceleration in humans had been observed in various studies, but disappeared on the careful analysis (of single-year cohorts in the US) in Gavrilov & Gavrilova (2011), it is natural to ask what causes this discrepancy – why was mortality deceleration observed?
Gavrilov & Gavrilova (2011) propose several causes; notably, in each instance when such a factor is corrected or diminished, the fit with the Gompertz law becomes better.
Relevance
The rates of late-life mortality are important for pensions. For example, the mortality rates in late life (after age 85) are of particular interest for the baby boom generation, which will reach this age starting in 2030, and for pensions funding calculations.
Late-life mortality rates are of basic importance for understanding aging, both for organisms generally and for humans specifically.
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