Lifetime Socioeconomic Position and Twins’ Health: An Analysis of 308 Pairs of United States Women Twins Nancy Krieger1*, Jarvis T. Chen1, Brent A. Coull2, Joe V. Selby3 http://medicine.plosjournals.org/archive/1549-1676/2/7/pdf/10.1371_journal.pmed.0020162-S.pdf