Thomas A. Trikalinos and Joseph Lau had the initial idea. Dr. Trikalinos designed the study and drafted the protocol with input from Dr. Lau. Dr. Trikalinos, Denish Moorthy, Winifred W. Yu, Jounghee Lee, and Mei Chung acquired the data. Dr. Trikalinos developed software for citation graph manipulation and analyses and wrote the first draft of the paper. All authors critically revised the paper. No other person including medical editors has assisted in any way in the writing or the preparation of the manuscript. Dr. Trikalinos had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.