[1] NHGRI, Neurobehav Clin Res Sect, Social & Behav Res Branch, Bethesda, MD 20892 USA
[2] NIMH, Bethesda, MD 20892 USA
[3] NIDA, Translat Addict Med Branch, Technol & Translat Res Unit, Baltimore, MD USA
[4] Univ Penn, Comp & Informat Sci, Philadelphia, PA 19104 USA
[5] NHGRI, Social Network Methods Sect, Social & Behav Res Branch, Bethesda, MD 20892 USA