DtotheG DtotheG - 4 months ago 12
SQL Question

SQL - STDEVP or STDEV and how to use it?

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

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.