Why N-1?

Home > Statistics Every Writer Should Know > The Stats Board > Discusssion

Why N-1?
Message posted by George Sykes (via 198.115.164.120) on March 17, 2001 at 6:08 PM (ET)

Why do you use N-1 as opposed to N in a formula to solve a standard deviation problem?

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: Why N-1?
Message posted by Phil (via 165.247.230.223) on March 18, 2001 at 12:12 AM (ET)

It is a mathematical statistics issue. The formula for the sample standard deviation with n-1 is "unbiased". You are using the results of a sample to estimate the standard deviation (sigma). Different estimators may have different properties.

An unbiased estimator has an expected value equal to the parameter of interest. The estimate with n-1 in the denominator is "unbiased".

I think this has been explained before in old threads, if you want to see some other explaintions.

Your $5 contribution helps cover part the $500 annual cost of keeping this site online.