An article in the Journal of Pharmaceutical Sciences discusses the change of plasma protein binding of diazepam at various concentrations of imipramine. Suppose the results were reported as follows.

Diazepam with Imipramine Diazepam Alone (1.25 mg/mL) 1.25 2.50 5.00 97.99 97.68 96.29 93.92 The values given represent mean plasma protein binding, and n  8 for each of the four groups.

Find the sum of squares among the four groups.