Eight things to know about the D-score

A measure of child development

Stef van Buuren: ‘it is a significant step towards a unified, universal measure of development, independent of the instrument used to evaluate individual children’. Iris Eekhout adds: ‘here are eight things to know about this remarkable metric’.

1. One scale, many applications

The D-score is a flexible scale that serves various groups effectively. Healthcare practitioners utilise it to monitor and assess patient development over time. Researchers benefit from its ability to integrate and analyse data from various sources, ensuring that diverse measures and milestones can be compared and aligned to support their studies. Policymakers find it invaluable for setting developmental goals and evaluating the effectiveness of health policies.

2. Single number for development, no separate domains

The D-score simplifies the evaluation of child development by focusing on the most pertinent milestones at each stage. During the early years, it places greater emphasis on motor skills, reflecting their critical role in early development. As children grow older, the focus shifts to verbal skills, which become more relevant. This automatic weighting of milestones ensures that the D-score remains a precise and practical tool throughout different stages of development.

3. Milestone difficulty is independent of age and population

The methodology defines the difficulty of developmental milestones, rather than by age, on the D-score scale. This approach enables comparisons not only among children of the same age and between different ages but also across diverse populations.

4. Universal norms across instruments

The D-score uses consistent units across different populations, enabling the creation of developmental charts similar to growth charts. Such a chart can help track a child’s development over time. These norms are based on population differences rather than variations between assessment tools.

5. Validated measurement approach

The D-score utilises the Rasch model, which maps the likelihood of achieving a developmental milestone to the increase in ability level. The model has been calibrated using a dataset involving over 60,000 children to accurately assign difficulty levels to more than 800 milestones. The Expected A Posteriori (EAP) algorithm then computes the D-score by determining the most probable point on the developmental scale, based on the child’s responses to milestones administered.

6. Measurement harmonisation

The D-score model holds milestones from more than 20 different instruments. Each instrument can have a different measurement purpose, such as signalling whether a child is falling behind in his development or assessing the current developmental state.

Instruments may also have different modes of administration, such as caregiver-reported milestones or milestones directly observed from the child. Assessments from each of these instruments can be transformed into a D-score. This enhances the comparability of historical data and enables meta-analysis, so investigators can make better use of existing data.

7. Our platform or yours

TNO has created various tools to facilitate the broad adoption of the D-score methodology. The JAMES platform allows practitioners to use the D-score to assess an individual child’s development. The dcalculator is a web application that enables researchers to upload their milestone data and download a D-score from these data, eliminating the need for specialist statistician support. There is also a dedicated R Package that simplifies the process of inputting either new or historical data to calculate a D-score.

8. Foundation for global standards

In a recent project, a TNO research group teamed up with groups from Harvard and the WHO to establish a single model for measuring childhood development across the globe. The D-score was chosen as the base metric for the Global Scale for Early Development (GSED) due to its simplicity, clarity, and accuracy. The GSED is a global, comprehensive assessment tool for assessing holistic development across multiple domains. Utilising the D-score, GSED clarifies the similarities and differences in childhood development across different countries and supports the United Nations’ Sustainable Development Goals for early child development.

Find out more

Are you a practitioner, researcher or policymaker interested in uncovering how the D-score can help you collect, clarify and compare early child development data for better child health, decision-making or research support? Yvette Fleming is happy to talk to you.

About TNO

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We are TNO. A safer, healthier, and more sustainable life. That's what we are all about. As an independent research organisation, we are the driving force behind innovation. We make knowledge serve the common good. Since 1932, it has been our mission to give the right answers – and to ask the right questions. For the world of today and tomorrow. By combining disciplines and domains, we can tackle the most complex questions. On the road to a better life and a brighter future.