Table 1.

Descriptive values of the included variables. Note. 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; s.d., standard deviation; α, Cronbach's α, 95% CI, 95% confidence interval. Note that the number of included individuals (n) is slightly lower for sub-domains of autistic traits compared with total autistic traits because more individuals exceeded the 20% of missing items in the sub-scales.

	no. of items	n	mean	s.d.	skew (skewa)	α (95% CI)
synaesthesia	8	4262	0.76	1.25	2.39 (1.16)	0.79 (0.78, 0.80)
total autistic traits	12	3998	1.91	1.62	1.31 (0.00)	0.71 (0.70–0.73)
RRBI-D	4	3483	0.92	0.88	1.04 (0.23)	0.62 (0.60–0.64)
SIC	8	3843	1.09	1.15	1.56 (0.40)	0.62 (0.60–0.64)

^aAfter log-transform.