Comparison of four statistical approaches to score child development: a study of Malawian children

Assessment of child development often results in a multitude of binary outcome data. There is no agreed way to use them to score the developmental status of children. Conventional methods include age-standardized Z-scores and simple sum of number of passes. Recently two approaches based on the Rasch model and the concept of 'developmental age' have been proposed. This study aims to compare the performance of the four approaches.

In a longitudinal study, 473 Malawian children were measured for growth status at age 36 months and administered a new test of developmental milestones between age 3 and 6 years. The test consisted of four domains: gross motor (GM), fine motor (FM), social and language development. The four approaches were used to score the developmental level of each child in each domain, and the results compared.

In this sample, the approach based on the Rasch model provided development scores that were more normally distributed than the other approaches did. The four sets of scores were highly correlated with each other. They gave similar estimates of the effect of height-for-age on GM, social and language development. In FM development, the maximum difference in the effect size estimates was only 0.04 standard deviation despite its statistical significance (P = 0.009).

The four approaches were practically equivalent in the context of the estimation of an intervention effect or association. Their relative advantages and disadvantages are discussed. None of them can be universally recommended.