)2. Often, the variance is estimated as [1/(n – 1)]Σi(Wi – )2, which is almost the same for n = 40 (see Chapter 28).NOTE 17B: The variances should be 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 n = 40 (see Chapter 28).