An Original Bayesian Longitudinal Model of Language Development Trajectories in Nigerian Children Across Socioeconomic Strata

Language development trajectories in Nigerian children are shaped by socioeconomic stratification in ways that interact with early childhood education quality, home language environment, and cultural stimulation practices, and developing an original Bayesian longitudinal model for characterising these trajectories provides a methodological and empirical contribution to both Nigerian ECD and developmental science. This study developed and estimated an original Bayesian hierarchical longitudinal model of language development trajectories in Nigerian children across socioeconomic strata. A multi-site longitudinal design enrolled 600 children from three socioeconomic strata (200 per stratum) in Lagos, Enugu, and Kano States at age 2.5 years and followed them to age 6 with 6-monthly assessments. Language development was assessed using the Community Inventory of Language Development in Igbo, Yoruba, Hausa, and English versions. Bayesian hierarchical growth curve models specified child-level, family-level, and community-level random effects with informative priors drawn from the Nigerian developmental literature. Individual trajectory heterogeneity was substantial within all three SES strata, confirming that SES is not deterministic of language development. High-quality ECD attendance significantly accelerated language development trajectories within all strata, with effect sizes largest in the lowest SES group. Home language richness mediated 44 percent of the SES-trajectory relationship. Zone-level differences in trajectory shapes reflected distinct cultural language socialisation patterns. The original Bayesian trajectory model identifies critical developmental windows for intervention impact maximisation. Expert review by 20 biostatistics and language development specialists confirmed the model's methodological originality and developmental validity.

Keywords: language development trajectories, Bayesian hierarchical model, Nigeria, socioeconomic strata, longitudinal study