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Table 2 Sample size, descriptive statistics, and phenotypic correlations

From: A longitudinal twin study of the association between childhood autistic traits and psychotic experiences in adolescence

Sample sizes
Age N families contacted MZM DZM MZF DZF DZOS
8 years 13,941 858 804 1046 874 1659
12 years 8438 814 775 1050 895 1601
14 years 11,118 529 463 662 548 911
16 years 10,874 738 686 1043 905 1560
Measure descriptive statistics
Measure Cronbach’s α Possible range of scores \( \overline{x} \) (SD) Skew
CAST age 8 0.71 0–31 4.85 (3.09) 0.99 (−0.64)
CAST age 12 0.73 0–30 4.62 (3.15) 1.24 (−0.48)
AQ age 14 0.80 0–87 36.78 (12.16) 0.24 (0.21)
AQ age 16 0.80 0–80 24.04 (10.62) 0.39 (0.36)
SPEQ paranoia 0.93 0–72 12.17 (10.62) 1.56 (−0.61)
SPEQ hallucinations 0.88 0–45 4.66 (6.01) 2.08 (0.22)
SPEQ cognitive disorganisation 0.77 0–11 3.96 (2.85) 0.44 (−0.63)
SPEQ grandiosity 0.86 0–24 5.32 (4.43) 1.19 (−0.41)
SPEQ anhedonia 0.78 0–50 16.36 (7.93) 1.14 (0.17)
SPEQ negative symptoms 0.86 0–27 2.63 (3.63) 2.32 (0.45)
Phenotypic correlations
  Autistic traits age 8 Autistic traits age 12 Autistic traits age 14 Autistic traits age 16
Paranoia .02 (ns) .06* .07** .10**
Hallucinations .07** .10** .13** .14**
Cognitive disorganisation .08** .12** .17** .21**
Grandiosity .04* .08** .04 (ns) .00 (ns)
Anhedonia .14** .18** .24** .30**
Negative symptoms .27** .32** .40** .47**
  1. All means are given for untransformed scores; skew values are shown for the untransformed measures, and then the standardised residuals used in analyses in parentheses. All Ns are number of twin pairs with data available at each age
  2. SPEQ Specific Psychotic Experiences Questionnaire, CAST Childhood Autism Spectrum Test, AQ Autism Spectrum Quotient, ns nonsignificant
  3. *p < .05; **p < .01