Measuring Autistic Traits in the General Population: A Systematic Review of the Autism-Spectrum Quotient (AQ) in a Nonclinical Population Sample of 6,900 Typical Adult Males and Females

Background:   The Autism-Spectrum Quotient (AQ) is a self-report measure of autistic traits. It is frequently cited in diverse fields from neuroimaging to epigenetics and has been used with adults of at least average intelligence with autism and to nonclinical controls. It has also been administered to other clinical groups such as those with schizophrenia, prosopagnosia, anorexia, and depression. However, there has been no systematic review of the AQ since its inception in 2001. 

Objectives:  The present study reports a comprehensive systematic review of the literature to estimate a reliable mean AQ score in individuals without a diagnosis of an autism spectrum condition (ASC), in order to establish a reference norm for future studies.

Methods: A systematic search of computerized databases was performed, to identify studies that administered the AQ to nonclinical participant samples representing the adult male and female general population. Inclusion was based on a set of formalised criteria that evaluated the quality of the study, the usage of the AQ, and the population being assessed.  

Results:   After selection, 73 articles, detailing 6,934 nonclinical participants as well as 1,963 matched clinical cases of ASC, were analysed. Mean AQ score for the nonclinical population was 16.94 [95% CI 11.6, 20.0], while mean AQ score for individuals with ASC was 35.19 [95% CI 27.6, 41.1]. In addition, in the non-clinical population, a sex difference in autistic traits was found,(males > females) although no sex difference in AQ score was seen in the clinical population. 

Conclusions:   These findings have implications for researchers measuring autistic traits in the general population. Here we confirm previous norms with more rigorous data, and for the first time establish average AQ scores based on a systematic review, for populations of adult males and females with or without ASC. The AQ has demonstrated utility for phenotyping in a range of study-types, from genetic to imaging to screening. Future researchers could avoid risk of bias by carefully considering the recruitment strategy for both clinical and non-clinical groups, and could demonstrate transparency by reporting recruitment methods for all participants.