ref: bb88573b7a75f9ec4faaac2e8934964f463c55ec
dir: /stt/variance.2.t/
Another definition of the variance of a variable X is...
.Bp
Another definition of the variance of a variable X is:
.EQ
s sup 2 = {sum from 0 to N ({X sub i} - {X highbar}) sup 2} over N
.EN
This is the arithmetic mean of the squared deviations from the mean.
Some books choose to introduce it this way,
and correct it by multiplying by N(N-1) in some situations.