WHYUSE

SUM

?

(N - 1)

Sigma²= Population variance = Sum (X - u)²

N

Desire to estimate this, using

instead of u

(sample mean instead of population mean)

Estimate (Sigma²) =

Est {Sum [(x -

- (u - x)]²}

N

Estimate (Sigma²) =

Est {Sum [(x -

- 2(x -

-

+ (u -

N

N

N