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Retrieved 14 October 2013. Check date values in: |access-date= (help) ↑ Hempel S, Newberry SJ, Maher AR, Wang Z, Miles JN, Shanman R, Johnsen B, Shekelle PG (9 May 2012).
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Retrieved 14 October 2013. ↑ Hempel S, Newberry SJ, Maher AR, Wang Z, Miles JN, Shanman R, Johnsen B, Shekelle PG (9 May 2012).