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Tag: natural experiments

Slavery, ethnic diversity and economic development

What is the impact of the slave trades on economic progress in Africa? Are the modern African states which ‘exported’ a higher number of slaves more likely to be underdeveloped several centuries afterwards? Harvard economist Nathan Nunn addresses these questions in his chapter for the “Natural experiments of history” collection. The edited volume is supposed to showcase a number of innovative methods for doing empirical research to a broader audience, and historians in particular. But what Nunn’s study actually illustrates is the difficulty of making causal inferences based on observational data. He claims that slave exports contributed to economic underdevelopment, partly through impeding ethnic consolidation. But his data is entirely consistent with a very different interpretation: ethnic diversity in a region led to a higher volume of slave exports and is contributing to economic underdevelopment today. If this interpretation is correct, it could render the correlation between slave exports and the lack of economic progress in different African states spurious – a possibility that is not addressed in the chapter. The major argument of Nunn’s piece is summarized in the following scatterplot. Modern African states from which more slaves were captured and exported (correcting for the size of the country) between the XVth and the XIXth centuries are associated with lower incomes per capita in 2000 (see Figure 5.1 on p.162, the plot reproduced below is actually from an article in the Quarterly Journal of Economics which looks essentially the same): The link grows only stronger after we take into…

Natural experiments of history? Not really, but still a fine book

Natural experiments are a fine (and fun) way to study questions where the researcher doesn’t have control over the assignment of cases. But the label ‘natural experiment’ can get abused – not all comparisons are ‘natural experiments’. Nature needs to intervene into the assignment of cases in a way that can be credibly regarded as random in order to approximate the experimental method (e.g. here). Jared Diamond and Paul Robinson have collected seven essays in a book entitled “Natural Experiments of History”. But from the seven studies, only one or two might be regarded as a true ‘natural experiment’ – the rest are just more or less systematic comparisons. It is still a fine book – I found all seven essays interesting and stimulating. But they are not natural experiments; in fact, Diamond and Robinson themselves seem to retract from the label in the concluding chapter of the book. For example, in his chapter Patrick Kirch studies Polynesian cultural evolution. The three islands of Mangaia, Marquesas, and Hawai”i end up with quite different social and political institutions despite being populated by the same people. To his credit, Kirch uses ‘controlled comparisons’ instead of ‘natural experiments’ to describe his approach. But does the fact that the three islands were settled by people coming from the same homeland in Western Polynesia allow us to ‘control’ for the pre-settlement characteristics of the people who inhabited Mangaia, Marquesas, and Hawai’i? The explorers leaving in search of new homes are seldom a representative sample from…

Emigrants vs. Settlers

In his contribution to ‘Natural Experiments in History‘ James Belich  argues that shifting attitudes towards emigration in Britain and the US were essential for the settler explosions in the American West, Australia, Canada, New Zealand and South Africa. Belich puts the shift in attitudes between 1810 and 1820 and illustrates the transformation with the contest between the use of ’emigrant’ and ‘settler’ on the pages of the Times of London. Always on the lookout for potential application of the awesome power of Google N-gram, I checked whether the shift of attitudes and vocabulary is visible in the larger body of English-language literature indexed  by Google N-gram as well. Here is the graph: ‘Settler’ gets more popular than ’emigrant’ indeed! But the shift occurs a bit later with an initial catch-up around 1930 and the ultimate win of ‘settler’ around 1970. Interestingly, in the corpus of British books, ‘settler’ never surpasses ’emigrant’ in popularity, while in American books the two terms are practically even between 1830 and 1865 when ‘settler’ overtakes ’emigrant’ for good. Actually, it is ‘pioneer’ that rises in popularity beyond ’emigrant’ around 1810 and then surpasses both ’emigrant’ and ‘settler’ after 1845: Overall, Belich’s transformation in attitudes and vocabulary towards emigration seems reflected in literature, although the shift occurs later, and is much stronger for American English.