Background and aims Explore the factor structure of the Social Communication Questionnaire (SCQ: Rutter et al., 2003) for primary school children 6–11 years, 7951 screened as part of an autism prevalence study identified with diagnosed developmental disorders including Autism Spectrum Disorders (ASDs).

Methods The SCQ is a 40-item parent report questionnaire that asks about characteristic autistic behaviour. It is based on the Autism Diagnostic Interview – Revised (ADI-R: Lord et al, 1994) recommended cut off score for ASDs ( >15). Sixty nine percent 5457 of parents completed the SCQ, 7% 411 were identified (males 294, 71%) with parent reported diagnosed developmental disorders: Speech and language 227, 55%; ADHD 64, 16%; ASDs 58, 14%; Dyspraxia 49, 12%; Downs Syndrome 8, 2% other diagnosis 5, 1%.

Results The optimal SCQ cut off score for differentiating ASDs from other developmental disorders was ( >13) sensitivity 0.89, specificity 0.81, PPV 0.43, NPV 0.98. Principal Components Analysis revealed 4 factors explaining 49% of the total variance. First factor, 32%: 7 of 10 items, Reciprocal Social Interaction (RSI) ADI-R domain. Second factor 9%, 6 of 8 Restricted Repetitive Stereotyped Behaviour (RRSB) domains third and fourth factors each explaining 4% variation. Four of 6 item’s on the third factor (RSI) domain, 4 of 5 on the fourth ADI-R Communication domain.

Conclusions A substantial number of communication items did not correlate well with the total score. These items should be revised for screening in a general population setting. Discriminative ability of the SCQ total score performed well for differentiating children with ASDs from other developmental disorders.