Using linear discriminant analysis to separate cases based on monoaminergic markers to determine the greatest influence on depression showed DAT (Wilks’ Lambda, 0.535, p = 0.0004) and D4DR (Wilks’ Lambda 0.442, p = 0.0002) in combination had greatest predictive values, showing 78% accuracy in re-classifying the original data. The gene discussed is SLC6A3; the disease is major depressive disorder.