Why parity matters
For any integer x, x² ≡ x (mod 2). So the sum of squares of a
set of integers always has the same parity as their sum. Combined with the constraint
that the mean must be reachable at all, this eliminates a large space of reported
standard deviations — often including ones that look entirely unremarkable.
What it can't see
GRIMMER knows nothing about your response scale. A standard deviation can pass GRIMMER and still be impossible because it exceeds what a 1–7 scale physically permits — that is the SPRITE bound, a separate check. Running both catches strictly more than either alone.
Read more
- GRIM calculator — the mean-only test
- statcheck, GRIM, GRIMMER, SPRITE — a field guide