Garcia R, Benet M, Arnau C, Cobo E. Efficiency of the cross-over design: an empirical estimation. Stat Med. 2004 Dec 30;23(24):3773-80. doi: 10.1002/sim.2072.
Sunyer J, Jarvis D, Pekkanen J, Chinn S, Janson C, Leynaert B, Luczynska C, Garcia-Esteban R, Burney P, Anto JM, European Community Respiratory Health Survey Study Group. Geographic variations in the effect of atopy on asthma in the European Community Respiratory Health Study. J Allergy Clin Immunol. 2004 Nov;114(5):1033-9. doi: 10.1016/j.jaci.2004.05.072