Ding R, McCarthy M, Desmond JS, Lee JS, Aronsky D, Zeger SL. Characterizing waiting room time, treatment time, and boarding time in the emergency department using quantile regression. Acad Emerg Med [Internet]. 2010 Aug [cited 2013 Jan 15];17(8):813–823. doi: 10.1111/j.1553-2712.2010.00812.x