“…Higher prevalence of moderate ID among male children has been reported, with males 1.6-1.9 times more likely to be classified with moderate ID than females (Croen, Grether, & Selvin, 2001;Drews, Yeargin-Allsopp, Decoufle, & Murphy, 1995;Richardson, Katz, & Koller, 1986), and these sex differences seem to increase with age up to 15 years (Wen, 1997). Factors that could play a role in sex differences for ID are X-linked conditions (Chelly & Mandel, 2001;Partington, Mowat, Einfeld, Tonge, & Turner, 2000;Tariverdian & Vogel, 2000), low birth weight and an association between low birth weight and low IQ in males (Matte, Bresnahan, Begg, & Susser, 2001;Zubrick et al, 2000), and maternal smoking, which has a proportionaly higher detrimental effect on males than females (Zaren, Lindmark, & Bakketeig, 2000).…”