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Voegtline KM, Stifter CA; Family Life Project Investigators.Voegtline KM, et al.Infant Behav Dev. 2010 Dec;33(4):545-54. doi: 10.1016/j.infbeh.2010.07.006. Epub 2010 Aug 21.Infant Behav Dev. 2010.PMID: 20732715Free PMC article.