Dear Tipsters,
The formula for sigma, the SD of the population requires N
If we only wish to know s, the SD of the sample, you can still use n.
But if you are trying to estimate sigma from s, you divide by n-1.
Why?
Because dividing by n give a biased estimate.
n-1 corrects for that and gives
that makes folks a little
more open to using them.
Just guessing,
Larry
> -Original Message-
> From: Jim Dougan [mailto:[EMAIL PROTECTED]]
> Sent: Monday, September 25, 2000 9:30 AM
> To: Larry Z. Daily
> Cc: TIPS
> Subject: RE: Another Standard Deviation question
>
Right - I know that. But, that has always been the case and we have only
recently been using the "N" formula at all. Look back ten years and you
will find that most texts never even introduce the "N" formula. McCall's
2001 edition (just released) still only uses the "N-1" formula.
Apparently
The N version of the formula is a descriptive statistic - it simply
describes the current sample (or population). The N-1 version is an
inferential statistic and takes into account degrees of freedom and the fact
that I've estimated the mean of the population.
Larry
*
I prefer the z-score formula for r for a number of reasons.
The name of the thing makes more sense (the first moment of the product of
z-scores, product-moment). Although this isn't obvious to students at first,
many appreciate this little bit of trivia.
The interpretation is more direct for tw
