The D-score: a metric for interpreting the early development of infants and toddlers across global settings

Ann M Weber; Marta Rubio-Codina; Susan P Walker; Stef van Buuren; Iris Eekhout; Sally M Grantham-McGregor; Maria Caridad Araujo; Susan M Chang; Lia Ch Fernald; Jena Derakhshani Hamadani; Charlotte Hanlon; Simone M Karam; Betsy Lozoff; Lisy Ratsifandrihamanana; Linda Richter; Maureen M Black; Working group members and data contributors

doi:10.1136/bmjgh-2019-001724

The D-score: a metric for interpreting the early development of infants and toddlers across global settings

BMJ Glob Health. 2019 Nov 19;4(6):e001724. doi: 10.1136/bmjgh-2019-001724. eCollection 2019.

Authors

Ann M Weber^{1

2}, Marta Rubio-Codina³, Susan P Walker⁴, Stef van Buuren^{5

6}, Iris Eekhout⁵, Sally M Grantham-McGregor⁷, Maria Caridad Araujo³, Susan M Chang⁴, Lia Ch Fernald⁸, Jena Derakhshani Hamadani⁹, Charlotte Hanlon^{10

11}, Simone M Karam¹², Betsy Lozoff¹³, Lisy Ratsifandrihamanana¹⁴, Linda Richter¹⁵, Maureen M Black^{16

17}; Working group members and data contributors

Collaborators

Working group members and data contributors:
Orazio Attanasio, Gary L Darmstadt, Bernice M Doove, Emanuela Galasso, Pamela Jervis, Girmay Medhin, Ana M B Menezes, Helen Pitchik, Sarah Reynolds, Norbert Schady

Affiliations

¹ School of Community Health Sciences, University of Nevada Reno, Reno, Nevada, USA.
² Department of Pediatrics, Stanford University School of Medicine, Stanford, California, USA.
³ Inter-American Development Bank, Washington, District of Columbia, USA.
⁴ Caribbean Institute for Health Research, University of the West Indies, Kingston, Jamaica.
⁵ Netherlands Organization for Applied Scientific Research TNO, Leiden, Netherlands.
⁶ Methodology & Statistics, Utrecht University, Utrecht, Netherlands.
⁷ Institute of Child Health, University College London, London, UK.
⁸ School of Public Health, University of California Berkeley, Berkeley, California, USA.
⁹ Maternal and Child Health Division, icddr,b, Dhaka, Bangladesh.
¹⁰ Institute of Psychiatry, Psychology and Neuroscience, Health Service and Population Research Department, Centre for Global Mental Health, King's College London, London, UK.
¹¹ Department of Psychiatry, WHO Collaborating Centre for Mental Health Research and Capacity Building, School of Medicine, and Centre for Innovative Drug Development and Therapeutic Trials for Africa (CDT-Africa), College of Health Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
¹² Department of Pediatrics, Federal University of Rio Grande, Rio Grande, Brazil.
¹³ Center for Human Growth and Development, University of Michigan, Ann Arbor, Michigan, USA.
¹⁴ Centre Médico-Educatif "Les Orchidées Blanches", Antananarivo, Madagascar.
¹⁵ Centre of Excellence in Human Development, University of the Witwatersrand, Johannesburg, South Africa.
¹⁶ Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland, USA.
¹⁷ International Education, RTI International, Research Triangle Park, North Carolina, USA.

Abstract

Introduction: Early childhood development can be described by an underlying latent construct. Global comparisons of children's development are hindered by the lack of a validated metric that is comparable across cultures and contexts, especially for children under age 3 years. We constructed and validated a new metric, the Developmental Score (D-score), using existing data from 16 longitudinal studies.

Methods: Studies had item-level developmental assessment data for children 0-48 months and longitudinal outcomes at ages >4-18 years, including measures of IQ and receptive vocabulary. Existing data from 11 low-income, middle-income and high-income countries were merged for >36 000 children. Item mapping produced 95 'equate groups' of same-skill items across 12 different assessment instruments. A statistical model was built using the Rasch model with item difficulties constrained to be equal in a subset of equate groups, linking instruments to a common scale, the D-score, a continuous metric with interval-scale properties. D-score-for-age z-scores (DAZ) were evaluated for discriminant, concurrent and predictive validity to outcomes in middle childhood to adolescence.

Results: Concurrent validity of DAZ with original instruments was strong (average r=0.71), with few exceptions. In approximately 70% of data rounds collected across studies, DAZ discriminated between children above/below cut-points for low birth weight (<2500 g) and stunting (-2 SD below median height-for-age). DAZ increased significantly with maternal education in 55% of data rounds. Predictive correlations of DAZ with outcomes obtained 2-16 years later were generally between 0.20 and 0.40. Correlations equalled or exceeded those obtained with original instruments despite using an average of 55% fewer items to estimate the D-score.

Conclusion: The D-score metric enables quantitative comparisons of early childhood development across ages and sets the stage for creating simple, low-cost, global-use instruments to facilitate valid cross-national comparisons of early childhood development.

Keywords: child development; global health; item response theory; psychometrics.

Grants and funding

WT_/Wellcome Trust/United Kingdom