ref: 3397ca132730e9a2eab364e149b35cd08def51ff
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:
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s sup 2 = {sum from 0 to N ({X sub i} - {X highbar}) sup 2} over N
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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.