Month of birth and child height in 40 countries

Abstract

Lokshin and Radyakin (2012) present evidence that month of birth affects child physical growth in India. We replicate these correlations using the same data and demonstrate that they are the result of spurious correlations between month of birth, age-at-measurement and child growth patterns in developing countries. We repeat the analysis on 39 additional countries and show that there is no evidence of seasonal birth effects in child height-for-age z-score in any country. Furthermore, we demonstrate that the Demographic and Health Survey data used to estimate the correlation is not suitable for the task due to a previously unrecognized source of measurement error in child month of birth. We document results from several papers that should be re-interpreted in light of this issue.

Correcting for artifactual correlation between misreported month of birth and attained height-for-age reduces but does not eliminate measured vulnerability to season of birth in poorer countries

“…Figure 1 demonstrates the effects of the linear adjustment for measurement error in child MOB across the whole sample. The solid line shows the steady increase in estimated coefficients of HAZ on child MOB across the year, an artifactual relation that was the result of random measurement error in child MOB (19, 20). The dotted line shows how these estimated coefficients changed after correcting for the random measurement error, eliminating the implausibly large gap in HAZs between December-born and January-born children.…”

“…Analyses of seasonality in child heights depend on the accurate measurement of child birthdates (19, 20). This is a difficult task, especially because globally only ∼65% of children aged <5 y have had their births registered (21).…”

“…Larsen et al (20) recently discovered artifacts that cause an apparent seasonal pattern in child heights by MOB in the Demographic and Health Surveys (DHS). One of these artifacts is a gradient in height-for-age z-scores (HAZ), observed as an implausibly smooth linear increase in average HAZ monthly from January to December, and an implausibly large step change in mean HAZ from those reportedly born in December of one year to January of the next (19, 20). HAZs indicate linear growth for individual children compared with healthy children of the same age and sex.…”

Are Poor Individuals Mainly Found in Poor Households? Evidence Using Nutrition Data for Africa

“…is measurement error in the nutritional outcomes. This could be particularly true for very young children, for which accurate anthropometric measurement can be difficult (Ulijaszek and Kerr 1999;Larson et al 2017;Agarwal et al 2017). We re-estimate the conditional probabilities for stunting and wasting for children 18 months and older only.…”

Can shorter mothers have taller children? Nutritional mobility, health equity and the intergenerational transmission of relative height

“…Also, the surveys we use are nationally representative but may face selection bias and low power among the most under-served populations (Comandini et al 2016), so for this study we address only the overall distribution and do not address subgroup differences. Third, there remains the possibility of statistical artifacts associated with the birth dates needed to compare child heights (Agarwal et al 2017, Larsen et al 2019, Finaret and Masters 2019a, so for this study we pool all birth months to ensure no effect of artifactual seasonality. A final contribution of our study related to data quality is to test the robustness of rankorder regression compared to direct tests of intergenerational transmission in the level of each variable.…”