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Ernstzen DV, Hillier SL, Louw QA.Ernstzen DV, et al. Among authors: hillier sl.BMC Med Res Methodol. 2019 Jun 28;19(1):134. doi: 10.1186/s12874-019-0771-3.BMC Med Res Methodol. 2019.PMID: 31253087Free PMC article.