Mentalising, also known as 'Theory of Mind', is the ability to understand and infer the cognitions of others, such as their perceptions, intentions, and beliefs. Although several tools have been designed to measure mentalising in adults, there exist methodological and practical limitations. Many of the existing measures conflate mentalising with similar constructs (e.g., empathy), and most are lengthy measures that are unsuitable for large population-based studies and clinical practice. These issues are currently hampering clinical and non-clinical investigations into mentalising and related social-cognitive abilities. Drawing on questionnaire measures of social cognition, we conceived a self-report mentalising scale, the Four-Item Mentalising Index (FIMI; Studies 1a & b). The FIMI was developed through a series of studies examining its factor structure and reliability (Studies 2a & b) and by testing its construct validity against a cognitive mentalising task, autistic traits, and comparing scores in autistic and non-autistic people (Studies 3a & b). Together, we demonstrate that the FIMI is a conceptually and methodologically robust tool for measuring mentalising ability in the general population, including autistic and non-autistic people. Future research directions and practical (clinical) applications of the scale are discussed, with a focus on improving understanding and management of (a)typical mentalising ability.

The 10-item Autism-Spectrum Quotient (AQ10) is a self-report questionnaire used in clinical and research settings as a diagnostic screening tool for autism in adults. The AQ10 is also increasingly being used to quantify trait autism along a unitary dimension and correlated against performance on other psychological/medical tasks. However, its psychometric properties have yet to be examined when used in this way. By analysing AQ10 data from a large non-clinical sample of adults (n = 6,595), we found that the AQ10 does not have a unifactorial factor structure, and instead appears to have several factors. The AQ10 also had poor internal reliability. Taken together, whilst the AQ10 has important clinical utility in screening for diagnosable autism, it may not be a psychometrically robust measure when administered in non-clinical samples from the general population. Therefore, we caution against its use as a measure of trait autism in future research.

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White and Remington (2019) found that autistic people may have increased anthropomorphic tendencies to ascribe human-like attributes to non-human agents. However, it was unclear from their study whether this relationship holds after accounting for socio-demographic variables known to be associated with anthropomorphism. The psychometric properties of the anthropomorphism questionnaire they used has also not been investigated, raising concerns about whether it measures the same construct in people with differing levels of autistic traits. Addressing these issues, we re-examined the relationship between autism and anthropomorphism in a large sample of adults ( N = 492). Conceptually replicating White and Remington, we found that autistic traits were significantly associated with greater anthropomorphic tendencies, even after accounting for age and sex (Study 1). Equally, psychometric concerns with the anthropomorphism questionnaire were revealed, leading us to refine this measure and re-analyse the data. A less clear-cut but significant association between autistic traits and anthropomorphism was found (Study 2). Our refined anthropomorphism measure also had improved psychometric properties, particularly showing that it is suitable for future autism research. Our findings are discussed in relation to individual differences in social-cognitive processing and we outline future directions for investigating mechanisms linking anthropomorphism and social cognition in autism. Lay abstract Anthropomorphism is the tendency to attribute human-like qualities (e.g. thoughts and feelings) to non-human entities (e.g. objects and weather systems). Research by White and Remington (2019) suggested that anthropomorphism is more common in autistic compared to neurotypical adults, which is interesting given that autistic individuals sometimes misunderstand the thoughts and feelings of other people. In this article, we re-examined the link between autism and anthropomorphism in a large sample of adults with varying degrees of autistic traits, with several important methodological advances on previous research. Across two studies, we found that individuals with more autistic traits reported greater anthropomorphic tendencies. As part of these analyses, we had to develop a new, refined measure of anthropomorphism, which showed better reliability and validity than the original measure. This measure will be useful in future autism-related research. Overall, advancing White and Remington’s study, these findings help us to better understand individual differences in socially relevant processes, including those that may be enhanced in autism (e.g. anthropomorphism).

Murphy et al. (2022) raised concerns regarding the validity of the Four-Item Mentalising Index (FIMI). We wholeheartedly agree with Murphy et al. that there are problems in the social cognition literature hampering research. However, we maintain the FIMI is conceptually grounded in empirical and theoretical research, and that concerns regarding its construct validity are overstated. Drawing on recent research, we also discuss issues concerning the interpretation of discriminant validity analyses and discuss approaches to improve objectivity in future research. Overall, we argue that the FIMI is a conceptually and psychometrically sound measure, which has utility in future social cognition research and clinical practice.