A new measure of social understanding in adolescents and adults reveals individual differences that are trait-like and interpretable.

The Birmingham Advanced Mindreading Stories (BAMS) test was developed and subject to psychometric evaluation as a new measure of social understanding. Narrative stimuli were co-produced with demographically diverse young people. Adolescent participants (aged 13-17 years) were tested in schools and adult participants (aged 18-34 years) were tested online. Study 1 (N=300) identified stories that could be coded reliably, that were sensitive to varying performance and that measured the same underlying “mindreading” factor. Study 2 (N=2612) collected data at three time points over 9 months. Confirmatory factor analysis and structural equation modelling provided evidence that the BAMS was sensitive, reliable, valid, and fair. Using the same data set, Study 3 showed that similarity of participants and authors influenced performance on the BAMS. Individual differences in social understanding corresponded to variation in the flexibility with which participants could mindread a diversity of people and situations.