Table 2.

Overview of the psychometric properties of the Systemizing Quotient (SQ) across countries

Study (sorted on year of appearance)	Country	Internal consistency (Cronbach’s α)	Test–retest reliability (Pearson r)	N (males)	Females M (SD)	Males M (SD)	Effect size of sex difference (Cohen’s d)
Baron-Cohen et al. (2003)a	UK	0.79	n.r.	278 (114)	24.1 (9.5)	30.3 (11.5)	0.59
Wakabayashi et al. (2007) control group b	Japan	0.88	n.r.	137 (71)	17.3 (10.9)	29.5 (10.4)	1.15
Wakabayashi et al. (2007) student group b	Japan	0.88	n.r.	1250 (616)	17.7 (9.0)	27.8 (11.8)	0.96
Wheelwright et al. (2006)c	UK	0.90	n.r.	1761 (723)	51.7 (19.2)/(27.7) f	61.2 (19.2)/(32.6) f	0.49
Ling et al. (2009)a	UK	0.83	n.r.	167 (84)	22.5 (8.5)	32.1 (10.4)	1.01
Van Horn et al. (2010)a	Sweden	n.r.	n.r.	299 (114)	23.9 (8.6)	31.7 (10.4)	0.82
Manson and Winterbottom (2012)a	UK	n.r.	n.r.	321 (133)	23.7 (9.6)	33.2 (11.6)	0.89
Wright and Skagerberg (2012)d	US	0.91-0.94	n.r.	5186 (?)	2.6 (0.37)	2.8 (0.38)	0.53
Zeyer et al. (2012)b	Switzerland	0.83	n.r.	500 (250)	17.7 (10.2)	28.4 (9.0)	1.11
Baron-Cohen et al. (2014)	UK	n.r.	n.r.	3906 (2562)	55.1 (21.1)/(29.4) f	68.1 (21.6)/(36.3) f	0.41
Present study	Netherlands	0.87	.79e	685 (270)	49.4 (15.3)/(26.3) f	61.9 (17.9)/(33.0) f	0.75

UK United Kingdom, N sample size, M mean, SD standard deviation

^aThe original 40-item (+20 filler item) version of the SQ was used

^bA shortened 40-item version of the revised SQ-R was used

^cThe revised 75-item SQ-R was used

^dThe 75-item SQ-R and a reworded variant (with negatively formulated items being rephrased positively) were used, and an alternative scoring method was used (mean of the 1, 2, 3, 4 Likert scale rating)

^eTest–retest period of 15 months (range 6–20 months)

^fRecalculated mean score for comparison with the original 40-item SQ (SQ = (SQ-R/75) × 40)