I thought the P in STDEVP stood for "Population", so STDEVP would be the estimated Population Standard Deviation (obtained by applying Bessel's correction to the actual Sample Standard Deviation) and STDEV the actual Sample Standard Deviation (in the SQL 2000 days you could look it up in BoL, so I never bothered to learn it - I wanted those functions rarely enough for it not to be worth making an effort to learn it); when I discovered that which is which isn't documented (at least not in any obvious manner) in BoL for SQL 2008 I just tried to work out which was which based on the name, and got it wrong because the SQL function names are misleading.

wolfkillj (1/28/2011)

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I think the "P" in STDEVP does stand for "population", as that function returns the actual standard deviation of the entire population (sometimes called the "n" method); hence, the standard deviation of a population consisting of a single value = 0, as STDEVP will return. STDEV returns the standard deviation with Bessel's correction applied (i.e., the estimated population standard deviation or the sample standard deviation, sometimes call the "n-1" method), which is why applying this function to a population consisting of a single value will not work.

Can anyone who knows the programmatic bases of STDEV and STDEVP confirm my conclusion?

mdv 9731 (1/28/2011)

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I do not agree that the answer is right.
Think it is supposed to be 0.

the standard deviation σ (sigma) is the square root of the average value of (X − μ)2.

Which means σ = sqrt(((1-1)^2)/1) = 0

Or in other words std. deviation equals sqrt of (population-avarage) sq / number of population values

Please correct me if im wrong on the formula it has been a while since i used my statistics