Correlations between factors generated from variables for different age ranges and for all ages (N = 13,138).

Factors derived from analysis of all ages: 1 Verbal ability, 2 Language acquisition, 3 Social understanding, 4 Semantic-pragmatic skills, 5 Repetitive Behaviour, 6 Articulation and 7 Social inhibition. Not all factors were identified for each age range. Hence, for example, the comparisons for the 6–15 m age range only show one factor and are only compared with the equivalent factor derived for 18–38 m and for all ages. This factor was not identified for age ranges 42–77 m and 81 m–9y.
At age 18–38 m, Echoes what said 38 m failed to load highly on any of the 5 factors identified for this age range but was included as a 6th ‘factor’ and used as a proxy for Factor 4.
At age 81 m–9y, an estimate of Factor 4 was calculated by summing two factors (2nd and 3rd factors, see Table S5 part D) derived from the factor analysis for this age range.
All correlations were highly significant (p<0.0001).