The variation among all the subjects in an experiment is measured by what is called sum of squares total or SST. SST is the sum of the squared differences of each score from the mean of all the scores. Letting GM (standing for "grand mean") represent the mean of all scores, then

SST = Σ(X - GM)²

where GM = ΣX/N and N is the total number of subjects in the experiment

For the example data:

N = 12

GM = (3+5+3+5+2+2+4+4+2+1+3+2)/12 = 3

SST = (3-3)²+(5-3)²+(3-3)²+(5-3)² + (2-3)²+(2-3)²+(4-3)²+(4-3)² + (2-3)²+(1-3)²+(3-3)²+(2-3)² = 18

The sum of squares due to differences between groups (SSB) is computed according to the following formula:

where n