Sample vs population standard deviation
Standard deviation measures how spread out your numbers are around the mean. A small value means the data clusters tightly; a large value means it's widely scattered. The only difference between the two versions is the divisor: population divides by n, while sample divides by n−1 (Bessel's correction) to better estimate a whole population from a sample.
Which should I choose?
- Choose sample when your numbers are a subset drawn from a larger group — this is the most common case and matches Excel's
STDEV.S. - Choose population only when your data covers every member of the group you care about.
Frequently asked questions
Why does sample standard deviation need at least two values?
Because it divides by n−1. With a single value that divisor is zero, so the sample standard deviation is undefined. Population standard deviation of one value is simply 0.
Is variance just standard deviation squared?
Yes. Variance is the average squared distance from the mean, and standard deviation is its square root — which is why standard deviation is in the same units as your data.
Does it handle decimals and negatives?
Yes. Mix whole numbers, decimals and negatives freely; non-numeric entries are ignored.