[nullsense]

And only 3 standard deviations is actually a disability?

[bsder]

2SD vs 3SD is a big deal in biological organisms.

If we look at height, that's a 6'7"/5'1" male or a 6'1"/4'8" female.

At those numbers, the probability that there is a medical issue--malnourishment/endocrine problems/Marfan's syndrome, etc.--starts being non-trivial.