Figure 2

Graphical representation of how Ferguson's δ 'works'. In this sample 30 subjects are uniformly distributed over a scale with 10 score categories (i), so that the frequency (f _i ) for all i scores is 3. The subjects are placed in a 10 × 10 matrix according to their scores. Each cell comprises f _i × f _j comparisons of f _i = 3 subjects with a certain score (e.g. '7') with f _j = 3 subjects with another score (e.g. '2') in the white cells, or with themselves in the shaded cells. Ferguson's δ relates the number of discriminating comparisons between subjects (within the white cells) to all comparisons (within all cells). See the text for the actual calculation of δ.