The Economic Effects of Childhood Speech and Language Difficulties: A Cross-Cohort Quantitative Life Course Analysis

Abstract

Introduction Early vocabulary and speech development predict poorer broader childhood skills, educational attainment, mental health, and employment. However, little is known beyond early adulthood about how language relates to income, non-cognitive skills, or physical health. Aims The thesis aims to utilise historical data to highlight the broad and enduring impact of early communication over the life course. Appropriate, evidence-based recommendations are established for research and clinical practice. Methodology Two datasets were selected, capable of modelling the importance of early communication skills on life chances. The Newcastle Thousand Families Study (1947) incorporates novel health visitor observation data from age two to seven of 881 children, identifying 161 with Speech, Language and Communication Needs. The British Cohort Study (1970) complements this analysis with a national dataset of thousands of children, containing a continuous assessment of receptive vocabulary at age five. Regression, mediation, and counter-factual econometric methods (Oaxaca-Blinder Decomposition and Regression Discontinuity Design) are utilised to maximise the value in the historical data. Findings SLCN is associated with introverted personality traits, and a reduced tendency to enjoy new experiences in later adulthood. Lower earnings and health were observed at age 50 but not age 62. Mediation analysis confirms the existence of a direct relationship between early receptive vocabulary and later earnings across adulthood. No significant mediation effect was observed through education or non-cognitive skills after accounting for this direct effect. However, when comparing income differences between high and low vocabulary groups (no direct effect of vocabulary), higher levels of educational attainment and cognitive skills were found in the high vocabulary group on average, explaining most of the observed group ii differences in income. Returns to these variables are not statistically different between vocabulary groups, implying that vocabulary does not moderate the importance of known drivers of income. In summary, it is disadvantage in early years rather than discrimination in adulthood which explains the income gap. Furthermore, whilst vocabulary scores predict a range of functional outcomes, this is not true over narrow thresholds. Small differences in language scores do not predict outcomes, regardless of the placement of the threshold, suggesting that thresholds are an unreliable method of identifying functional language disorders. Therefore, strictly applied thresholds should be removed from clinical diagnoses, and academic research should reduce its reliance on unsupported distinctions. Conclusion Varying methodological approaches and data enable the illustration of substantial positive associations between early verbal communication skills and a range of previously unmeasured lifelong outcomes.