where the bar over p (pronounced "p bar") indicates n an average and the ^ means summing each of the i=1

F observations starting with the first (there are a total of n, as indicated above the summation symbol, which is an upper-case "sigma"), and n is the sample size. The variance is an average of the square of how much each observation differs from the mean. The variance is taken by summing the squared differences between each estimate and the average and then dividing by one less than the sample size:

The square in the numerator comes about because (pt - p) for observations less than the mean will be

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