Stunting: past, present, future

Child malnutrition is a very important global health challenge. 155 million children globally suffer from malnutrition and are consequently stunted, much shorter than healthy children at the same age. Reducing stunting was an important target in the Millenium Development Goals and is also a target under Goal 2 of the Sustainable Development Goals. This report summarises recent research on child stunting that was presented and discussed at a conference, STUNTING: PAST, PRESENT AND FUTURE, at the London School of Economics and Political Science in September 2017. The conference brought together academics across a wide range of disciplines with policy experts and influencers from the third sector. There were four key lessons that participants took away from the conference. First, stunting was present in currently developed countries at the beginning of the twentieth century, which suggests that reductions in stunting were a corollary to the secular increase in mean adult height across the twentieth century. Second, there needs to be more research on catchup growth in adolescence to determine whether catch-up growth in height is also associated with improvements in other dimensions of health and human capital that are affected by malnutrition, for instance cognitive deficiencies. If interventions in adolescence can be effective, then it may be possible to mitigate some of the consequences of stunting for already stunted children. Third, researchers need to be aware of the large degree of spatial variation in stunting within countries and the distinct age pattern of stunting between ages 0 and 5 when trying to understand why children become stunted. Fourth, participants agreed that more interdisciplinary collaboration is necessary to design experiments and models to capture the multi-dimensional nature of child stunting

Sample selection biases and the historical growth pattern of children

Bodenhorn et al. (2017) have recently sparked considerable controversy by arguing that the fall in adult stature observed in military samples in the United States and Britain during industrialisation was a figment of sample selection bias. While subsequent papers have questioned the extent of the bias (Komlos and A’Hearn 2016; Zimran 2017), there is renewed concern about selection bias in historical anthropometric datasets. This paper extends Bodenhorn et al.’s discussion of selection bias on unobservables to sources of children’s growth, specifically focussing on biases that could distort the age pattern of growth. Understanding how the growth pattern of children has changed is important since these changes underpinned the secular increase in adult stature and are related to child stunting observed in developing countries today. However, there is potential for selection on unobservables in historical datasets containing children’s and adolescents’ height, so scholars must be aware of these biases before analysing these sources. This paper highlights, among others, three common sources of bias: 1) positive selection of children into secondary school in the late nineteenth and early twentieth centuries; 2) distorted height by age profiles created by age thresholds for enlistment in the military; and 3) changing institutional ecology which determines to which institutions children are sent. Accounting for these biases weakens the evidence of a strong pubertal growth spurt in the nineteenth century and raises doubts on some long run analyses of changes in children’s growth, especially for Japan

The effect of nutritional status on historical infectious disease morbidity: evidence from the London Foundling Hospital, 1892-1919

There is a complex inter-relationship between nutrition and morbidity in human health. Many diseases reduce nutritional status, but on the other hand, having low nutritional status is also known to make individuals more susceptible to certain diseases and to more serious illness. Modern evidence on these relationships, determined after the introduction of antibiotics and vaccines, may not be applicable to historical settings before these medical technologies were available. This paper uses a historical cohort study based on records from the London Foundling Hospital to determine the causal effect of nutritional status of children, proxied by weight- and height-for-age Z-scores, on the odds of contracting five infectious diseases of childhood (measles, mumps, rubella, chicken pox and whooping cough) and on sickness duration from these diseases. I identify a causal effect by exploiting the randomisation of environmental conditions as foundling children were removed from their original homes, then fostered with families in counties nearby London and later returned to the Foundling Hospital’s main site in London. I find no effect of nutritional status on the odds of contracting the five diseases, but I do find a historically important and statistically significant effect of nutritional status on sickness duration for measles and mumps. These findings have three implications. First, historical incidence of these diseases was unrelated to nutritional status, meaning that poor nutritional status during famines or during the Colombian Exchange did not affect the spread of epidemics. However, undernutrition in these events may have exacerbated measles severity. Second, improving nutritional status in the past 150 years would have reduced the severity of measles and mumps infections but not affect the decline in whooping cough mortality. Finally, selective culling effects from measles would be larger than those from whooping cough since whooping cough severity was not correlated with underlying nutritional status

A Classroom Experiment on Exchange Rate Determination with Purchasing Power Parity

We develop a classroom experiment on exchange rate determination appropriate for undergraduate courses in macroeconomics and international economics. Students represent citizens from different countries and need to obtain currency to purchase goods. By participating in a sealed bid auction to buy currency, students gain a better understanding of currency markets and the determination of exchange rates. The implicit framework for exchange rate determination is one in which prices are perfectly flexible (in the long run) so that purchasing power parity (PPP) prevails. Additional treatments allow students to examine the impact of transport costs, nontradable goods and tariffs on the exchange rate and to explore possible deviations from PPP.

Did smallpox cause stillbirths? Maternal smallpox infection, vaccination and stillbirths in Sweden, 1780-1839

Woods (2009) argued that smallpox was an important cause of stillbirths in the past. While there is strong evidence that maternal smallpox infection could lead to fetal loss, it is not clear whether smallpox infections were a demographically important source of stillbirths. In this paper, we use parish-level data from the Swedish Tabellverket dataset from 1780 to 1839 to test the effect of smallpox on stillbirths quantitatively. We use two empirical strategies: dynamic panel regressions that test the instantaneous effect of smallpox epidemics on stillbirths; and a continuous treatment difference-in-difference strategy to test whether the reduction in smallpox prevalence following vaccination led to a larger decrease in the stillbirth rate in parishes where smallpox was more prevalent before vaccination. We find very little evidence that smallpox infection was a major cause of stillbirths in history. Our coefficients are largely insignificant and close to zero. This is because the vast majority of women contracted smallpox as children and therefore were no longer susceptible during pregnancy. We do find a small, statistically significant effect of smallpox on stillbirths from 1820-39 when waning immunity from vaccination put a greater share of pregnant women at risk of contracting smallpox. However, the reduced prevalence of smallpox limited the demographic impact. Thus, smallpox was not an important driver in historical stillbirth trends and did not contribute to in utero scarring effects for cohorts born when smallpox prevalence was high

Sample-selection biases and the historical growth pattern of children

Bodenhorn et al. (2017) have sparked considerable controversy by arguing that the fall in adult stature observed in military samples in the United States and Britain during industrialization was a figment of selection on unobservables in the samples. While subsequent papers have questioned the extent of the bias (Komlos and A'Hearn 2019; Zimran 2019), there is renewed concern about selection bias in historical anthropometric datasets. Therefore, this article extends Bodenhorn et al.'s discussion of selection bias on unobservables to sources of children's growth, specifically focusing on biases that could distort the age pattern of growth. Understanding how the growth pattern of children has changed is important because these changes underpinned the secular increase in adult stature and are related to child stunting observed in developing countries today. However, there are significant sources of unobserved selection in historical datasets containing children's and adolescents' height and weight. This article highlights, among others, three common sources of bias: (1) positive selection of children into secondary school in the late nineteenth and early twentieth centuries; (2) distorted height by age profiles created by age thresholds for enlistment in the military; and (3) changing institutional ecology that determines to which institutions children are sent. Accounting for these biases adjusts the literature in two ways: evidence of a strong pubertal growth spurt in the nineteenth century is weaker than formerly acknowledged and some long-run analyses of changes in children's growth are too biased to be informative, especially for Japan

Children's growth in an adaptive framework: explaining the growth patterns of American slaves and other historical populations

This article presents a new adaptive framework for understanding children's growth in the past. Drawing upon the recent work on adaptive responses in relation to growth, it presents prenatal and postnatal adaptive mechanisms that affect the growth patterns of children. The most novel adaptive response to the historical literature is the prenatal predictive adaptive response where the metabolism and growth trajectory of a child is programmed to match predicted conditions later in life. Having discussed the framework in detail, a reinterpretation of the growth pattern of American slaves is then suggested. It seems likely that a mismatch between relatively good conditions in utero and absolutely appalling conditions in infancy and early childhood led slave children to become extremely stunted by the age of three or four. However, after this age, slave children experienced catch‐up growth because their immune systems had become more developed and because their diet improved tremendously and hookworm exposure was reduced. Thus, it seems that American slave children may have experienced substantial catch‐up growth because they were prenatally programmed for a higher metabolism and growth trajectory. The article concludes by setting out some stylized facts about children's growth in the past and pointing toward areas of future research

Health, gender and the household: children’s growth in the Marcella Street Home, Boston, MA and the Ashford School, London, UK

This paper is the first to use the individual level, longitudinal catch-up growth of boys and girls in a historical population to measure their relative deprivation. The data is drawn from two government schools, the Marcella Street Home (MSH) in Boston, MA (1889-1898) and the Ashford School of the West London School District (1908- 1917). The paper provides an extensive discussion of the two schools including the characteristics of the children, their representativeness, selection bias and the conditions in each school. It also provides a methodological introduction to measuring children’s longitudinal catch-up growth. After analysing the catch-up growth of boys and girls in the schools, it finds that there were no substantial differences between the catch-up growth by gender. Thus, these data suggest that there were not major health disparities between boys and girls in late nineteenth century America and early twentieth century Britain

Imaging a Quasar Accretion Disk with Microlensing

We show how analysis of a quasar high-magnification microlensing event may be used to construct a map of the frequency-dependent surface brightness of the quasar accretion disk. The same procedure also allows determination of the disk inclination angle, the black hole mass (modulo the caustic velocity), and possibly the black hole spin. This method depends on the validity of one assumption: that the optical and ultraviolet continuum of the quasar is produced on the surface of an azimuthally symmetric, flat equatorial disk, whose gas follows prograde circular orbits in a Kerr spacetime (and plunges inside the marginally stable orbit). Given this assumption, we advocate using a variant of first-order linear regularization to invert multi-frequency microlensing lightcurves to obtain the disk surface brightness as a function of radius and frequency. The other parameters can be found by minimizing chi-square in a fashion consistent with the regularized solution for the surface brightness. We present simulations for a disk model appropriate to the Einstein Cross quasar, an object uniquely well-suited to this approach. These simulations confirm that the surface brightness can be reconstructed quite well near its peak, and that there are no systematic errors in determining the other model parameters. We also discuss the observational requirements for successful implementation of this technique.Comment: accepted to ApJ for publicatio