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Variance

Variance is the measure of statistical dispersion, that is, the variation among the different samples in a data set.  It is the average of the squared differences from the mean .

Variance is the square of the standard deviation .  If you do not know the standard deviation, you can use the following procedure to determine the variance.

Procedure for Finding the Variance:

1 .  Find the mean of the scores ( x ¯ ) .

2 .  Subtract the mean from each individual score ( x x ¯ ) .

3 .  Square each of the differences obtained above.  ( x x ¯ ) 2 .

4 .  Add all of the squares obtained in step 3 . ( ( x x ¯ ) 2 ) .

5 .  Divide the total from step 4 by the number ( n 1 ) , where n is the total number of scores used.