Research

Micronutrients, Child Health and Later-Life Education: Evidence from Wartime Disruption of Iodized Salt in Ethiopia (Job Market Paper)

Ethiopia’s historically high rates of iodine deficiency was largely eliminated through universal salt iodization implemented since 1990s. However, iodine status deteriorated drastically when Ethiopia’s access to iodized salt was cut off by outbreak of the Ethiopia-Eritrea war in 1998. This study examines the impacts of early-life loss of iodized salt on children’s health and performance on standardized university-entrance exams. I use new spatial data on soil and crop iodine as direct measure of environmental iodine exposure linked to nationally representative health surveys and the country’s largest educational achievement database. I use difference-in-differences (DiD) strategy to compare changes in outcomes of cohorts who experienced the disruption earlier or later in life, in districts with low versus high soil iodine. I find that early-life loss of iodized salt is linked to lower educational achievement, particularly among children who grew up in iodine deficient districts. Post-war, children who resided in districts with the lowest soil iodine scored 0.09 SD lower relative to those who grew in districts with marginally higher soil iodine. Moreover, I find that children who were born post-war and resided in low iodine districts had lower weight for their age and suffer from higher cumulative morality incidence. The adverse effects are more pronounced in females and increase in severity the longer children were exposed to the disruption. Placebo tests and a variety of alternative specifications support causal link from iodine rather than other factors. The sudden loss and slow return to iodized salt in Ethiopia, combined with spatial variation in soil iodine, provides one of the largest scale tests of how iodine deficiency affects human development, with clear implications for micronutrient fortification policies.

Working Papers

Sibling rivalry between twins: Sex-specific differences in birthweight, child growth and survival across 72 low- and middle-income countries (Link

Robel Alemu, Amelia B. Finaret and William A. Masters

 This study tests for male-female differences in twins’ survival and health outcomes associated with the sex of their co-twin, using birthweights, anthropometry and mortality to isolate gestational factors from care practices after each child is born. Our data come from a wide range of low- and middle-income settings, based on the 191,838 twins among 1.7 million births recorded in 214 nationally representative Demographic and Health Surveys for 72 countries between 1990 and 2016. We find that drawing a male as opposed to a female co-twin is associated with lower birthweight and survival probability, but only for male infants. Worse health outcomes for male-male twin pairs could be linked to hormone levels or other interaction effects in utero; we observe no significant differences of co-twin sex on heights and weights, which could be due to gender bias favoring the surviving male children. 

Publications

Bai, Y., Alemu, R., Block, S. A., Headey, D., & Masters, W. A. (2021). Cost and affordability of nutritious diets at retail prices: Evidence from 177 countries. Food policy, 99, 101983.

Many policies and programs aim to bring nutritious diets within reach of the poor. This paper uses retail prices and nutrient composition for 671 foods and beverages to compute the daily cost of essential nutrients required for an active and healthy life in 177 countries around the world. We compare this minimum cost of nutrient adequacy with the subsistence cost of dietary energy and per-capita spending on all goods and services, to identify stylized facts about how diet cost and affordability relate to economic development and nutrition outcomes. On average, the most affordable nutrient adequate diet exceeds the cost of adequate energy by a factor of 2.66, costing US$1.35 per day to meet median requirements of healthy adult women in 2011. Affordability is lowest in Sub-Saharan Africa. The sensitivity of diet costs to each requirement reveals the high cost of staying within acceptable macronutrient ranges, particularly the upper limit for carbohydrates. Among micronutrients, total diet costs are most sensitive to requirements for calcium as well as vitamins A, C, E, B12, folate and riboflavin. On average, about 5% of dietary energy in the least-cost nutrient adequate diets is derived from animal source foods, with small quantities of meat and fish. Over 70% of all animal products in least-cost diets is eggs and dairy, but only in upper-middle and high-income countries. In lower income countries where egg and dairy prices are significantly higher, they are replaced by larger volumes of vegetal foods. When controlling for national income, diet costs are most significantly correlated with rural travel times and rural electrification. These data suggest opportunities for targeted policies and programs that reduce market prices and the cost of nutritious diets, while improving affordability through nutrition assistance, safety nets and higher earnings among low-income households.

Masters, W. A., Rosenblum, N. Z., & Alemu, R. G. (2018). Agricultural transformation, nutrition transition and food policy in Africa: Preston curves reveal new stylised facts. The journal of development studies, 54(5), 788-802.

This paper uses a Preston Curve approach to test for changes over time in agriculture, nutrition and food policy, comparing national averages in Africa and elsewhere at each level of national income per capita from the 1990s to the 2010s. Our statistical tests and data visualisations reveal that, at each level of income, African countries have faster rural population growth, a larger share of workers in agriculture and lower agricultural labour productivity than countries elsewhere, with no significant shift in these patterns from the 1990s to the 2010s. In contrast, there have been structural shifts towards less child stunting everywhere, and towards more adult obesity in high-income countries. The overall pattern of African governments’ food policies and government expenditures have not shifted, however, as they continue price interventions and low investment levels characteristic of low-income countries around the world.

Alemu, R., Gelaw, A. M., Gashu, D., Tafere, K., Mossa, A. W., Bailey, E. H., … & Lark, R. M. (2022). Sub-sampling a large physical soil archive for additional analyses to support spatial mapping; a pre-registered experiment in the Southern Nations, Nationalities, and Peoples Region (SNNPR) of Ethiopia. Geoderma424, 116013.

The value of physical archives of soil material from field sampling activities has been widely recognized. If we want to use archive material for new destructive analyses to support a task, such as spatial mapping, then an efficient sub-sampling strategy is needed, both to manage analytical costs and to conserve the archive material. In this paper we present an approach to this problem when the objective is spatial mapping by ordinary kriging. Our objective was to subsample the physical archive from the Ethiopia Soil Information System (EthioSIS) survey of the Southern Nations, Nationalities and Peoples Region (SNNPR) for spatial mapping of two variables, concentrations of particular fractions of selenium and iodine in the soil, which had not been measured there. We used data from cognate parts of surrounding regions of Ethiopia to estimate variograms of these properties, and then computed prediction error variances for maps in SNNPR based on proposed subsets of the archive of different size, selected to optimize a spatial coverage criterion (with some close sample pairs included). On this basis a subsample was selected.This is a preregistered experiment in that we have proposed criteria for evaluating the success of our approach, and are publishing that in advance of receiving analytical data on the subsampled material from the laboratories where they are being processed. A subsequent short report will publish the outcome. The use of preregistered trials is widely recommended and used in areas of science including public health, and we believe that it is a sound strategy to promote reproducible research in soil science.