Code and data from: No evidence for squaring the survival curve; lifespan-extending treatments increase variation in age-at-death

Geroscience has the goal of extending lifespan through geroprotective
interventions. These interventions are typically imparted on groups, with
their efficacy judged by increases in the average age-at-death. A more
equitable outcome, which looks beyond the average, is to attain a long
life for all individuals, such that the average age-at-death is high while
variability is low. This goal of increasing the mean while reducing
variation is sometimes referred to as “squaring the survival curve”. A
recent meta-analysis of vertebrate data found that dietary restriction
(DR) and the DR-mimetic, rapamycin, generally increase the average
age-at-death, while metformin (also considered a DR-mimetic) is less
effective. We have re-analysed this recently published data to study the
effects of lifespan-extending treatments on variation in the age-at-death.
On average, all three treatments increase the variance in the
age-at-death, but not the coefficient of variation (i.e.,
standard-deviation relative to the mean). This suggests that
lifespan-extending treatments do not reduce variance and “square the
survival curve”. Rather, any gains in mean age-at-death are matched by
corresponding increases in variation. Interestingly, this result is
consistent with the treatments proportionally reducing both the
age-dependent and age-independent parameters in a Gompertz-model of
mortality.