GSED Core Model: A Unified D-score Scale for Early Child Development From Seven Sites

The diversity of measures used to assess early childhood development complicates comparison across studies, populations, and programs. The Global Scales for Early Development (GSED) address this challenge by providing interoperable long and short forms (GSED-LF and GSED-SF) linked through a shared measurement model to a common developmental metric, the D-score. This article presents an updated GSED core model based on Rasch analysis of data from seven sites ( n = 9,287 children aged 0–41 months). The final model includes 281 items selected through item- and person-fit evaluation and shows improved measurement precision compared with earlier keys. Descriptive age-conditional reference curves derived from combined GSED-LF and GSED-SF data provide a methodological benchmark for typical development. We further demonstrate how external measures, including the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III), can be mapped onto the D-score scale by anchoring new items to the core model. D-scores and Development-for-Age Z-scores (DAZ) derived from GSED-LF, GSED-SF, and BSID-III show strong agreement, supporting the validity of the extension. The resulting GSED2510 key, implemented in the open-source dscore R package, enables standardized, measure-independent assessment of early child development.