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Graham L, Wright J, Walwyn R, Russell AM, Bryant L, Farrin A, House A.Graham L, et al.BMC Med Res Methodol. 2016 Oct 6;16(1):132. doi: 10.1186/s12874-016-0236-x.BMC Med Res Methodol. 2016.PMID: 27716063Free PMC article.Review.