Tutorial on how to understand degrees of freedom and why n-1 is used instead of just n for sample variance. Includes the reason why n-1 is use for a sample, but for the population variance. Video includes a visual and numerical example. The n-1 is used to adjusted the variance because of the error between the sample mean and the population mean.
Video on How to Calculate Standard Deviation
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Created by David Longstreet, Professor of the Universe, MyBookSucks