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Ramirez ER, Norman GJ, Rosenberg DE, Kerr J, Saelens BE, Durant N, Sallis JF.Ramirez ER, et al.J Adolesc Health. 2011 Apr;48(4):379-85. doi: 10.1016/j.jadohealth.2010.07.013. Epub 2010 Oct 15.J Adolesc Health. 2011.PMID: 21402267Free PMC article.