Wednesday, July 31, 2013

GG91, 6.2, the need for a critical attitude to mathematical models of lifespan

GG91 discussed several instances of 'blatant errors' in 6.2.

The first is EA Murphy 1978, "Genetics of longevity in man". Murphy78 proposed a $k$ subsystems in a serial configuration, and each subsystems break down after $n$ random damages. GG91 shows an error of differentiation in the published results.

The second example is Skurnick and Kemeny, 1978, Mechanisms of Ageing and Development. SK78 argued that 'an organism' as a 'chain' whose strength is determined by the 'weakest link'. GG91 connected SK78 with the 'Bingo model'. SK78 used the extreme value distributions. SK78 inferred the Weibull model of aging and Gompertz model in old ages.  GG91 stated that SK78's approximation of Gompertz model is incorrect because maximum approximation rule was used for minimum approximation. GG91 argues that this is a case that intuition and common sense would prevent such errors from happening.

The third example is Koltover 1983, Progress in Modern Biology. Koltover83 argued that death of an organism is the result of damage to at least one of the $Q$ blocks of genes in the genome. GG91 described this assumption as 'stupidity', because GG91 argued that every cell has its own genome.  This critique seems to be a misplaced because K83 model can be viewed as a 'genetic interaction model', which is commonly used in evolutionary genetics.

K83 used $m_c$ for a critical value of 'disfunction' and seems to be deterministic in nature and lead to simulanenous death of a homogeneous population. K83 then introduced heterogeneity using a truncated exponential distribution to describe different populations.

The fourth example is Witten 1985, Mechanisms of Ageing and Development. GG91 shows that the derived Gompertz coefficient in W85 cannot be positive if its assumption were also positive. In other words, W85 seemed to be working on a exponential growth model if the final Gompertz derivation holds.



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