The Strehler-Mildvan correlation from the perspective of a two-process vitality model

Area of Science:

• Demography
• Gerontology
• Biostatistics

Background:

• The Strehler-Mildvan (SM) theory explains Gompertz's law of mortality.
• It predicts a log-linear relationship (SM correlation) between Gompertz coefficients.
• Recent data show a breakdown of this correlation in developed countries, necessitating reassessment.

Purpose of the Study:

• To explain the SM correlation and its recent breakdown.
• To propose a new mechanism based on a two-process vitality model.
• To link mortality changes to distinct trends in extrinsic and intrinsic factors.

Main Methods:

• Utilized a newly developed two-process vitality model.
• Analyzed mortality data considering asynchronous trends in acute and chronic mortality factors.
• Examined historical mortality changes in the 20th century.

Main Results:

• The study explains the SM correlation through the interplay of acute and chronic mortality factors.
• The breakdown of the SM correlation is attributed to asynchronous changes in these factors.
• Mortality changes in the first half of the 20th century were driven by reducing immediate hazards.
• Changes in the second half were driven by a slower deterioration of intrinsic survival capacity.

Conclusions:

• The two-process vitality model successfully explains the SM correlation and its breakdown.
• Asynchronous trends in acute (extrinsic) and chronic (intrinsic) mortality factors are key.
• This provides a refined understanding of ageing and mortality dynamics.