Question 1

When do I use sample variance vs. population variance?

Accepted Answer

Use sample variance (dividing by n-1) when your data is a subset of a larger population. Use population variance (dividing by n) only when your data includes every member of the group you are studying. Most real-world data is a sample, so sample variance is the safer default.

Question 2

Why does sample variance divide by n-1 instead of n?

Accepted Answer

This is Bessel's correction. When you estimate the mean from the same data, you lose one degree of freedom. Dividing by (n-1) compensates for this, making the sample variance an unbiased estimator. If you divided by n, the sample variance would systematically underestimate the true population variance.

Question 3

What does the include zeros toggle do?

Accepted Answer

By default, zero values are treated as empty placeholders and excluded from the calculation. If zero is a real data value in your set (like a test score of 0 or a temperature reading of 0), toggle this on so zeros are included in the mean and variance calculations.

Question 4

What if I have more than 8 data values?

Accepted Answer

For larger data sets, you can use the related Variance Calculator which accepts summary statistics (Σx, Σx², and n). Compute those sums in a spreadsheet and enter them directly.

Sample Variance Calculator

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