A map is only worth trusting if the pattern holds up under hard questions. Here is what we measured, how we built the burden groups, and the checks that show the gradient is real — not just older people, and not a fluke of the data.
Everything is built from a large, trusted U.S. government health survey called NHANES (the National Health and Nutrition Examination Survey). For each person, NHANES collects far more than one doctor usually sees at once. We use three kinds of information from the same person:
Normally these live in separate places, so no one sees them together. We combine them into a single burden score for each person — the higher the score, the more these signals are off at once.
We line everyone up by their burden score, lowest to highest, and cut the line into five equal groups (statisticians call these “quintiles”). Group 1 is the lowest burden; group 5 is the highest. These are simply groups along a scale — not diagnoses, and not clusters the computer “found.” We chose the sorting up front so it can’t be tuned to produce a nice-looking answer.
The obvious objection to any “sicker group” finding is that the sicker group is just older, and older people have more chronic illness. So we tested exactly that.
In plain terms: even when we compare people of the same age, sex, race, and body weight, the highest-burden group still carries far more chronic illness. Age matters too — it is a real co-driver — so we say the burden gradient is independently associated with chronic illness, not that it is independent of age. Being honest about that is the point.
It shows up across age bands, too. Younger adults have lower rates overall, but the same climb from low to high burden. In the oldest group the rate is high everywhere, so the gradient flattens — a ceiling effect, and exactly what you’d expect if the score is measuring something real.
| Age group | Lowest burden | Highest burden |
|---|---|---|
| 20–39 | 22% | 48% |
| 40–59 | 32% | 69% |
| 60+ | 73% | 84% |
A single national average can hide a lot. A level of fatigue that looks “normal” against everyone may be clearly high for a young woman. That is why the tools let you compare against your own age and sex, not just the average American — so the burden a general “normal” would hide becomes visible.
OR = 2.45
(95% CI 1.92–3.12, p = 4.4e-13), adjusting for age, sex, race/ethnicity, and BMI. Per-quintile
trend OR = 1.23; per-SD burden OR = 1.41; age alone OR = 2.19 per SD
(a genuine co-driver). The full script, data manifest, and validation outputs are kept in a self-contained, reproducible source project (available to reviewers on request).