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# YouTubeT2-5 Variance of a discrete random variable

#### Nicole Seaman

##### Director of FRM Operations
Staff member
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The variance is a key measure of dispersion, it is the expected value of the squared difference between each value and the mean. The population variance is the "true" variance, but realistically in most cases, we have a sample (rather than a population) such that our unbiased estimate of the variance divides by (n-1) rather than n (n gives us an MLE).