Low language capacity in childhood: A systematic review of prevalence estimates.

What is already known on the subject Epidemiological research has informed our understanding of the origin and impact of low language capacity in childhood. Childhood language disorder is met with a rich history of evolving terminology and diagnostic guidelines to identify children with low language skills. Inconsistent definitions of and methods to identify low language in children have resulted in variable prevalence estimates in population-based studies. Variability in prevalence estimates impacts advocacy efforts to inform social, health and educational policy for child language disorder. What this study adds A total of 19 studies published at the time of this review aimed to provide estimates of the proportion of children who experience low language skills. Prevalence estimates varied between 0.4% and 25.2%, with more stable estimates reported in studies of older school-age children and those which utilised standardised assessments of both expressive and receptive language. Few studies utilised assessments of functional impact of language difficulties, which is misaligned with updated diagnostic criteria for child language disorder. What are the clinical implications of this work? This review reports substantial variability in estimates of the proportion of children and adolescents who live with low language skills. This variability underscores the importance of applying updated diagnostic criteria to identify the prevalence low language in childhood. Efforts to estimate the prevalence of low language must include measures of functional impact of low language skills. This aligns with clinical recommendations, which call for routine assessment of functional outcomes. To this end, we require a unified understanding of the term 'functional impact' in the context of low language, including the development and evaluation of measures that assess impact across emotional, social and academic domains.