Link to original article

Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Potatoes: A Critical Review, published by Pablo Villalobos on May 10, 2022 on The Effective Altruism Forum. Executive summary Nunn and Qian study the effect of the introduction of potatoes in the Old World on population growth between 1700 and 1900. We think the paper credibly establishes that between one-sixth and one-quarter of the growth is a consequence of the introduction of potatoes. The main reason for doubt is the possibility of spurious correlation due to spatiotemporal autocorrelation and the fact that potatoes were mainly grown in Europe, which at the time was experiencing growth due to unrelated factors. After performing several tests to account for these concerns, we conclude they are not strong enough to reject the conclusion of the paper. Introduction During the 18th and 19th centuries we saw rapid urbanisation and a drastic increase of population throughout the world. Some attribute this to industrialization; Nunn and Qian argue that we owe that to potatoes. They are not coy about it either. “According to our most conservative estimates, the introduction of the potato accounts for approximately one-quarter of the growth in Old World population and urbanisation between 1700 and 1900”. They back their hypothesis with data from several natural experiments, studying variability of city populations and adult heights between and within countries, and relate it to the timing when potatoes were introduced in different places. In this article we will summarise, replicate and critically review Nunn and Qian’s paper. We follow the methods established in (Sevilla, 2021) to study whether their findings are robust and whether they successfully establish a causal relation. Paper Summary The study purports to evaluate the causal impact of the introduction of potatoes in the Old World in population growth and urbanisation rates. The theory is that potatoes are more nutritious and provide 3x more calories per acre, so when they started being cultivated in the Old World they produced a positive shock in agricultural productivity, enabling higher populations and wealth per capita. A previous study by (Mokyr, 1981) estimated the causal effect of potatoes on population growth in Irish counties in 1845, finding an effect size of 0.7. This implies counties with high potato cultivation grew an extra 0.15% that year, compared to counties with low cultivation. In comparison, Nunn and Qian’s study uses data of the whole Old World, from 1300 to 1900, instead of just Ireland in a single time slice, and looks at urbanisation rates in addition to population. To estimate the causal impact of potatoes, the authors exploit two sources of variation on each country’s ability to grow potatoes: the time of introduction and the suitability of the land for potato cultivation. In their baseline analysis they find that around a quarter of the growth in population and urbanisation rates in that time period can be attributed to potatoes. The main pitfall of this strategy is that it relies on there being no other shocks during that time which are correlated with suitability for cultivation. Unfortunately, Europe is much more suitable for potato cultivation than other Old World regions, and the potato was introduced at the same time when Europe was diverging from other countries due to several unrelated factors. To check that the effect is indeed causal, the authors use several strategies: Adding several controls for alternative drivers of population and economic growth. Comparing only countries within the same continent Comparing cities within the same country Comparing the heights of soldiers in France, using their town of birth to estimate the importance of potatoes in their childhood diet. In all of those cases, they find a significant effect of potatoes on the outcome. For the within-continen...