Excel like a finance pro.
Statistical function
STDEV.S
Returns the standard deviation of a sample.
When to use it
Sample standard deviation: how spread out the data is, using n-1 in the denominator because you are estimating from a sample. This is the one to use for almost all business data.
The shape of it
- Syntax
=STDEV.S(number1, [number2], ...)
Worked examples
Eight values
=STDEV.S(2,4,4,4,5,5,7,9) → 2.13808994
Mean 5, sum of squared deviations 32, divided by 7, square root.
Monthly volatility
=STDEV.S(B2:B13) → 1,420
Month-to-month variability in a year of sales.
Coefficient of variation
=STDEV.S(B2:B13)/AVERAGE(B2:B13) → 0.142
The coefficient of variation: spread relative to the mean.
Worth knowing
- Use STDEV.P when your data is the entire population, not a sample.
- Use STDEV.P only when the range is the entire population.
- Z-score of a value: (x - AVERAGE)/STDEV.S.
- Volatility of returns is STDEV.S of the period returns, scaled by SQRT(periods per year).
Where it goes wrong
- #DIV/0! with fewer than two numbers.
- Text and blanks are ignored, so the sample size is smaller than the range.
Related
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