Urban JD, Clarke WP, von Zastrow M, Kobilka B, Nichols DE, Weinstein H, Javitch JA, Roth BL, Christopoulos A, Sexton PM, Miller KJ, Spedding M, and Mailman RB. 2007. Functional selectivity and classical concepts of quantitative pharmacology. J. Pharmacol Exp Therap. 320 (1): 1-13.