Figure 1.

Three-state model of morbidity and mortality. Individuals are born into State 1, and transitions between states i and j occur at age-specific hazard rates h_ij(a), where a is age in years. The transition between States 1 and 3 follows the baseline Gompertz-Makeham hazard function h₁₃(α)=α₁₊α₂ exp(βα), and the proportional term associated with a particular stress marker, k₂, acts to modify this baseline rate for those who die from State 2. The hazard of developing a detectable stress marker is set equal to the constant. k₁ (Redrawn from Usher 2000.)