INS and major depressive disorder: The hierarchical cluster analysis of the OS (2642 patients) yielded six clusters (195–626 patients each) based on the semipartial R2 that measures the homogeneity of merged clusters [11] with the following clustering variables: gender, age, insulin use, BMI, past or current medical history of depression, pregabalin monotherapy, prior use of gabapentin, baseline pain score, and baseline PRSI score.