@article {6115, title = {A universal evolutionary index for amino acid changes}, year = {2004}, pages = {1548-1556}, doi = {10.1093/molbev/msh158}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15140949}, author = {Hua Tang and Gerald J. Wyckoff and Jian Lu and Chung-I Wu} }