SQL - STDEVP or STDEV and how to use it?

Question

I have a table:

LocationId OriginalValue Mean 1          0.45         3.99   2          0.33         3.99 3          16.74        3.99 4          3.31         3.99 

and so forth...

How would I work out the Standard Deviation using this table and also what would you recommend - STDEVP or STDEV?

Answer 1

To use it, simply:

SELECT STDEVP(OriginalValue) FROM yourTable 

From below, you probably want STDEVP.

From here:

STDEV is used when the group of numbers being evaluated are only a partial sampling of the whole population. The denominator for dividing the sum of squared deviations is N-1, where N is the number of observations ( a count of items in the data set ). Technically, subtracting the 1 is referred to as "non-biased."

STDEVP is used when the group of numbers being evaluated is complete - it's the entire population of values. In this case, the 1 is NOT subtracted and the denominator for dividing the sum of squared deviations is simply N itself, the number of observations ( a count of items in the data set ). Technically, this is referred to as "biased." Remembering that the P in STDEVP stands for "population" may be helpful. Since the data set is not a mere sample, but constituted of ALL the actual values, this standard deviation function can return a more precise result.