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Dimitra Politi

Research papers:

Labyrinth


The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States (joint with James Feyrer and David N. Weil)

Journal of the European Economic Association, forthcoming

[link to paper]

[Online Appendix]

[Replication files]

Abstract

Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the US by taking advantage of this natural geographic variation. Salt was iodized over a short period of time beginning in 1924. We use military data collected during WWI and WWII to compare outcomes of cohorts born before and after iodization in localities that were naturally poor and rich in iodine. We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. Our results can explain roughly one decade's worth of the upward trend in IQ in the US (the Flynn Effect). We also document a large increase in thyroid-related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency.

Selected press coverage: The New Yorker, Freakonomics Blog, Business Insider




The effects of the generalized use of iodized salt on occupational patterns in Switzerland.

[link to paper]

Abstract

I estimate the long-term impact of the first large-scale nutritional supplementation program, salt iodization, which took place in Switzerland in the 1920s and 1930s. Iodized salt improved the health environment in utero, and it eradicated mental retardation caused by insufficient iodine intake. By exploiting variation in the pre-existing prevalence of iodine deficiency, as well as differences in the timing of the intervention across Swiss cantons, I show that cohorts born in previously highly deficient areas after the introduction of iodized salt were more likely to enter top-tier occupations with higher cognitive demands. As a result, wages of these cohorts were higher, accounting for about 1.9% of annual median earnings, or 2% of GDP per capita in 1991.




The Impact of Iodine Deficiency Eradication on Schooling: Evidence from the Introduction of Iodized Salt in Switzerland. 

[updated version coming soon]

Abstract

I study the impact of salt iodization in Switzerland on graduation rates. The programme, which began in 1922 and continues to this day, was the first wide-reaching nutritional intervention ever to take place. Iodine deficiency in utero causes mental retardation, and correcting the deficiency is expected to increase the productivity of a population by increasing its cognitive ability. The exogenous increase in cognitive ability brought about by the iodization program is also useful in the context of disentangling the effects of innate ability and education on later-life outcomes. I identify the impact of iodization on graduation rates by exploiting pre-existing geographic variation in the prevalence of iodine deficiency, as well as spatial and temporal variation in the introduction of iodized salt across Swiss cantons. By looking at sharp, discontinuous increases in iodized salt circulation I show that the eradication of iodine deficiency in previously deficient areas significantly increased graduation rates from upper secondary and tertiary education. My results are robust to falsification tests and different measures of iodine deficiency.