Roberts J, Price J, Nelson LM, Burchinal M, Hennon E, Barnes B. Receptive vocabulary, expressive vocabulary, and speech production of boys with fragile X syndrome in comparison to boys with Down syndrome. Am J Ment Retard. 2007 May 1;112:177-93.
Poole WK, Pollack M, Rapoport I, Williams V, Koch MA, Rao AV, Bartel DA. Use of Multivariate Methods in Quantifying the Variability in the Perception of Neonatal Intensive Care Unit Characteristics in Nine Hospitals in the Washington, DC Area: the NIH-DC Initiative to Reduce Infant Mortality in Minority Populations in the District of Columbia. Interstat. 2002 Jan 1.