Random errors cause LLMDs and LLMPs.

(a) Introducing random age-reporting errors into a log-linear model of mortality (solid black line) artificially lowers the age-specific probability of death qx (points) in late life, causing LLMD and LLMPs (dotted lines). (b) These simulated effects often reflect late-life mortality patterns observed in real data, for example, shown here in Jeanne Calment’s birth cohort (orange). Introducing age-coding errors by randomly reassigning individuals between observed cohorts (b) further increases rates of mortality deceleration, (c) increases proportionally larger errors in the calculated probability of death, and (d) greatly reduces the probability of death at advanced ages. Exact effect of errors calculated at a probability p = 0.001 (grey) and p = 0.0001 (black), data in (a) fitted by locally smoothed splines (dashed lines). Underlying data can be found in S2 Data. LLMD, late-life mortality deceleration; LLMP, late-life mortality plateau.