Open problems · P3
Separating ageing, cohort and survival
Cross-sectional age gradients mix true within-person change with birth-cohort differences and the selective survival of healthier people. Of 123 markers, 110 drift with age cross-sectionally. How much of that is real movement?
Why it matters
The landscape's sense of direction comes from age drift. If most of it is cohort or survival bias, the predicted paths are wrong.
What exists
- Cross-sectional percentiles by age (NHANES, HRS).
- Within-person 4-year change in HRS for 13 measures.
- Terminal-decline curves in the years before death.
A first step
Compare cross-sectional and within-person slopes measure by measure in HRS, and model the gap as a function of mortality selection.