A standard deviation seems like a simple enough concept. It’s a measure of dispersion of data, and is the root of the summed differences between the mean and its data points, divided by the number of data points…minus one to correct for bias.

This is, I believe, the most oversimplified and maddening concept for any learner, and the intent of this post is to provide a clear and intuitive explanation for Bessel’s Correction, or n-1.

Heliometer for Measuring Stellar Parallax, First Achieved by Friedrich Wilhelm Bessel, Public Domain

To start, recall the formula for a population mean:

Population Mean Formula

What about a sample mean?

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