Every school in the explorer gets a single number, the Demographic Shift Index. It answers one plain question: between the two chosen years, what share of a school's students would have to be a different race or ethnicity for the earlier year's makeup to match the later year's?
A score of 0 means the makeup didn't change at all. A score of 100 means it changed completely — not one part of the mix stayed the same. Most New Jersey schools, over a span of a few years, land somewhere in the single digits.
Take a school of 100 students. Here is its racial and ethnic makeup in two years. (With 100 students, each share is also a head count, which keeps the arithmetic simple.)
| Group | 2015 | 2025 | Change |
|---|---|---|---|
| White | 50% | 30% | −20 |
| Black | 30% | 30% | 0 |
| Hispanic | 10% | 25% | +15 |
| Asian | 10% | 15% | +5 |
| Native Am. | 0% | 0% | 0 |
| Sizes of the changes, added up | 40 |
Halve that total: the Shift Index is 20.
Three things moved between 2015 and 2025: the White share fell 20 points, the Hispanic share rose 15, and the Asian share rose 5. Add up the sizes of those moves, ignoring whether each was a gain or a loss, and the total is 40. Then take half of it. The Shift Index is 20: about 20 of every 100 students would have to be a different race for the 2015 mix to look like the 2025 mix.
Why halve it? Because every share that leaves one group has to land in another — the shares always add to 100%. The 20 points White lost are the very same 20 points that Hispanic and Asian gained. Counting both the leaving and the arriving counts that movement twice; halving the total fixes the double-count and leaves the real figure.
The index runs from 0 to 100. Some anchors for what a score means:
That last one is the ceiling: a school that is 100% White in the first year and 100% Hispanic in the second scores exactly 100 — White falls 100, Hispanic rises 100, the sizes add to 200, and half of that is 100. There is nowhere further to move.
The index compares shares, not raw numbers, so a school that simply grows or shrinks is not mistaken for one that changed character. A school that doubles from 300 students to 600 while keeping the exact same racial proportions scores 0 — its makeup is identical, there is just more of it. Enrollment still appears next to every school, though, because a sharp jump or drop in the same window is often the clue to what caused a shift: a rezoning, a closure, a new housing development.
The Shift Index measures how much a makeup moved, not which way. A school going from mostly White to mostly Hispanic and a school going the other direction register the same size of change. It is not a measure of "more diverse" or "less diverse," and it does not favor any group — it is a yardstick for the amount of change. The colored dot and the per-group figures beside each school show the direction; the index gives the magnitude.
The index measures across as many groups as both chosen years actually tracked. When both years fall in 2006–07 or later — the point at which the state began recording "two or more races" and counting Pacific Islander on its own — it uses all seven: White, Black, Hispanic, Asian, Pacific Islander, Native American, and two or more races. When the range reaches back before that, it falls back to the five groups held steady across the whole period — White, Black, Hispanic, Asian (folded together with Pacific Islander), and Native American — and sets "two or more" aside, so a comparison that crosses that line isn't thrown off by a category one of its years structurally could not have had. Either way the shares are rescaled to add to 100%. The data explainer walks through that history.
A single number cannot explain itself. The index says a school changed; it does not say whether that was a slow drift, as families move in and out over years, or a one-time event, like a rezoning, a grade reconfiguration, or a school closing and its students landing elsewhere. A sudden enrollment swing in the same window is often the tell. Small schools also move more on a handful of students, so a very small school can post a big score from ordinary year-to-year noise — raising the minimum-enrollment filter steadies the comparison. And the index is whole-school: it does not look inside at particular grades or programs.
In symbols, the index is ½ · Σ |change in each group's share| — half the sum of the absolute changes. Statisticians know this quantity as the total variation distance between two distributions; here it is simply "how much the mix moved."
