Table 2.

Twin correlations. Note. Twin correlations (how much each trait correlates between twins of a pair) and cross-twin–cross-trait (CTCT) correlations in sub-samples of monozygotic (MZ) and dizygotic (DZ) twins, extracted from the constrained, saturated bivariate models. Synaesthesia, synaesthesia screening score; RRBI-D, sub-scale of the A-TAC assessing repetitive behaviours, restricted interests and attention to detail; SIC, sub-scale of the A-TAC assessing social and communication difficulties.

	MZ	DZ
bivariate: synaesthesia and total autistic traits
synaesthesia	0.48 (0.42–0.53)	0.21 (0.16–0.26)
total autistic traits	0.44 (0.37–0.49)	0.21 (0.15–0.26)
CTCT	0.11 (0.07–0.16)	0.06 (0.02–0.10)
bivariate: synaesthesia and RRBI-D
synaesthesia	0.48 (0.42–0.53)	0.21 (0.16–0.26)
RRBI-D	0.35 (0.28–0.43)	0.17 (0.11–0.23)
CTCT	0.14 (0.09–0.19)	0.06 (0.02–0.10)
bivariate: synaesthesia and SIC
synaesthesia	0.48 (0.42–0.53)	0.21 (0.16–0.26)
SIC	0.47 (0.41–0.53)	0.16 (0.10–0.21)
CTCT	0.08 (0.03–0.13)	0.03 (0.01–0.07)