How do you calculate a variance?

Calculate variance by finding the average of the square of the data values' differences from the mean. You need the data values, mean, squared mean difference and the number of data values in the data set.

1. Find the data values

   Determine the values of each of the items in the data set.

2. Calculate the mean of the data values

   Calculate the mean of the data values by dividing their summation by the number of data values in the data set. If the data set is a, b, c, d, e, then the mean is (a + b + c +d + e)/5 since there are five data values in the set.

3. Determine the mean differences

   Calculate the mean differences by subtracting the mean from each data value. If the mean is m, then the mean differences are a - m, b - m, c - m, d - m and e - m.

4. Square the mean differences

   Multiply each square difference by itself. For the mean differences a - m, b - m, c - m, d - m and e - m, then the squared differences are (a - m)2, (b - m)2, (c - m)2, (d - m)2,and (e - m)2.

5. Calculate the variance

   Find the average of the squared differences by dividing their summation by the number of data values. For the squared differences (a - m)2, (b - m)2, (c - m)2, (d - m)2,and (e - m)2, the variance is [(a - m) 2 + (b - m) 2+ (c - m) 2 + (d - m) 2 + (e - m) 2]/5.