)2. Often, the variance is estimated as [1/(n – 1)]Σi(Wi – )2, which is almost the same for large n (see Box 28.4).NOTE 17F: The variance is calculated as the average squared deviation from the mean (1/n)Σi (Wi – )2. Often, the variance is estimated as [1/(n – 1)]Σi(Wi – )2, which is almost the same for large n (see Box 28.4).