What’s normal? The conceptual, statistical, and logistical challenges of creating global norms for early childhood development

• In Event: Addressing inequality in ECD

Proposal

This paper reviews the ongoing efforts of the World Health Organization to create global norms for child development using the Global Scales of Early Development (GSED). The proposed global norms for child development will describe the average trajectory of development for young children as well as show the degree to which a population varies around that mean. Global norms could allow for large improvements in meaningful monitoring of ECD status internationally and improved reporting against SDG 4.1.2.

Global norms have played an important role in the global health sector, with the tracking of stunting (low Height-for-Age Z-score) and Wasting (low Weight-for-Age Z-score) as essential health indicators in any country health surveillance system. These norms were established after evidence showing that a population of young children not facing nutritional or environmental constraints demonstrate similar patterns in their skeletal growth and weight gain, regardless of the country or culture from which they come (de Onis & Onyango, 2008). More recent work suggests that we may find similar patterns in the attainment of developmental milestones (Ertem et al., 2018; Villar et al., 2019).

The GSED’s new six-country study aims to build on this work by aiming to create a Development-for-Age (DAZ) score based on a diverse sample of children living without significant environmental challenges. This panel examines the many theoretical, practical, and methodological challenges creating global norms poses and discusses how the GSED project is addressing them.

The theoretical challenges discussed in this paper are centered on the assumption of conditional independence that undergirds the entire effort to build valid global norms. This assumption states that children who are free from nutritional or environmental constraints grow and develop at similar trajectories regardless of their culture, context, and language. Additionally, this assumption states that the variance around the expected age-dependent means is similar across countries and cultures. We discuss this central assumption, the process of selecting strict exclusion criteria, and how we plan to test this assumption before proceeding with global norms.

We then review the statistical challenges of global norm creation. We discuss the decisions made regarding sampling approach and the pros and cons of a longitudinal and cross-sectional sample, the means through which we calculated an adequate sample size, and the Generalized Additive Models of Location, Scale, and Shape (GAMLSS) process we use to determine an adequately fitting distributional description of scores by age (Stasinopoulos & Rigby, 2007).

We conclude the paper by discussing the practical and logistical challenges that a global norming study creates, how we plan to incorporate more data from opportunistic sites, and future plans of GSED including updating guidance around pre-term correction factors.

Authors

• Jonathan Seiden, Harvard University

• Abbie Raikes, University of Nebraska, College of Public Health

• Kenji Kitamura, Harvard University Graduate School of Education

• Dana Charles McCoy, Harvard Graduate School of Education