Variance calculation

[xlzheng]

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When calculate he variance, why do we divided with “n - 1” instead of divided by “n”, the equation please see the attached image.

Thanks!

[Deepti_Prasad]

n-1 is used when we are calculating sample variance instead of population variance. so when we calculate the sample mean of the variance the n-1 compensate for the true population.
Also considering the degree of freedom i.e. number of independent variables used to estimate the population variance is consider n-1, we use n-1 instead of n