Statistics



The variance is a numerical index describing the dispersion of a set of scores around the mean of the distribution. The variance is calculated as the average of the squared deviations from the mean.
There are two versions of variance; the population variance, usually denoted by , and the sample variance, usually denoted by s^{2}. Formula for population variance: Formula for Sample variance: Steps to find the variance: A couple has six children whose ages are 6, 8, 10, 12, 14 and 16. Find the variance in ages. Step 1. Work out the population mean. Step 2 and 3. For each number subtract the mean and then square the result. Work out the average of those squared differences. There's a more efficient way to calculate the standard deviation for a group of numbers, shown in the following equation: That is:
A couple has six children whose ages are 6, 8, 10, 12, 14 and 16. Find the variance in ages. The sample mean is: and Then The variance of a frequency distribution is given by: The following table gives the frequency distribution of the number of computers sold during the past 30 weeks at a computer store.
Calculate the variance. Solution:
The mean number of computers sold per week was 9 computers.
Properties:
