A Concurrent Validity Study of the Mullen Scales of Early Learning (MSEL) and the MacArthur-Bates Communicative Developmental Inventory (CDI) in Infants with an Elevated Likelihood or Diagnosis of Autism.

The study only assessed infants at 14 months, so it is unknown if these moderate correlations hold true for older toddlers or younger infants. The MSEL testers were aware of the infants' familial risk status (elevated vs. typical) during assessment, which could have introduced bias, although the authors state standardised training was used to minimise this. The sample was drawn entirely from Western, educated, industrialised, rich, and democratic (WEIRD) societies, limiting generalisability to other cultural contexts. Socio-economic status was not perfectly matched between the groups, which could influence language outcomes. The MSEL was translated for non-English speaking sites but was not normed for those specific populations, potentially affecting validity.

The study was funded by the H2020 Marie Skłodowska-Curie Actions, the Dutch Ministry of Education, Culture and Science, the Netherlands Organisation for Scientific Research, the National Science Centre of Poland, and the Innovative Medicines Initiative 2 Joint Undertaking. No commercial conflicts of interest with test publishers were declared.

Do not conclude that the MSEL is a better or more accurate tool than the CDI. The moderate correlation between them reflects that they measure different aspects of early language (behavioural communication vs. vocabulary size) at this young age, rather than one being invalid. The fact that the CDI did not distinguish elevated-likelihood from typical-likelihood infants does not mean it is insensitive; it may simply reflect that vocabulary differences are not yet apparent at 14 months in this at-risk group.