“…Contrary to the beliefs held by many substantive researchers, simulation research indicates that results from IRT models can be nontrivially biased when the true population distribution is nonnormal (Abdel-fattah, 1994;Boulet, 1996;de Ayala & SavaBolesta, 1999;DeMars, 2003;Kirisci, Hsu, & Yu, 2001;Seong, 1990 ;Stone, 1992; van den Oord, 2005;Zwinderman & van den Wollenberg, 1990). Specifically, MML estimates of item parameters increase in bias as the distribution deviates further from normality (Boulet, 1996;Stone, 1992;Woods, 2006Woods, , 2007aWoods, , 2007bWoods, , 2008Woods & Lin, 2009;Woods & Thissen, 2006).…”