The nutrition transition and agricultural transformation: a Preston curve approach

The nutrition transition in diets and health is closely tied to other aspects of economic development, including agricultural transformation and urbanization as well as demographic change and epidemiological transition from infectious to noncommunicable disease. Over time, dietary patterns typically shift from widespread inadequacy of many foods and nutrients, especially for children and mothers, into surplus energy intake and rising obesity with continued inadequacy of healthier foods. Diet‐related diseases remain the largest single cause of premature death and disability in all regions. This article combines food availability and dietary intake data from more than 100 countries over 30 years with a wide range of other evidence to characterize the nutrition transition and its association with changes in agricultural production and the food environment, asking how future dietary patterns might be steered toward healthier outcomes as national incomes grow.     

On the size distortion of tests after an overidentifying restrictions pretest

In the linear instrumental variables model, we provide theoretical and Monte Carlo evidence for the size distortion of a two‐stage hypothesis test that uses a test of overidentifying restrictions (OR) in the first stage. We derive a lower bound for the asymptotic size of the two‐stage test. The lower bound is given by the asymptotic size of a test that rejects the null hypothesis when two conditions are met: the test of OR used in the first stage does not reject and the test in the second stage rejects. This lower bound can be as large as 1 ? ε_P, where ε_P is the pretest nominal size, for a parameter space that allows for local non‐exogeneity of the instruments but rules out weak instruments. Copyright © 2011 John Wiley & Sons, Ltd.