Although economists have long been aware of Jensen's inequality, many econometric applications have neglected an important implication of it: under heteroskedasticity, the parameters of log-linearized models estimated by OLS lead to biased estimates of the true elasticities. We explain why this problem arises and propose an appropriate estimator. Our criticism of conventional practices and the proposed solution extend to a broad range of applications where log-linearized equations are estimated. We develop the argument using one particular illustration, the gravity equation for trade. We find significant differences between estimates obtained with the proposed estimator and those obtained with the traditional method. Copyright by the President and Fellows of Harvard College and the Massachusetts Institute of Technology.

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Why is GDP growth so much more volatile in poor countries than in rich ones? We identify four possible reasons: (i) poor countries specialize in more volatile sectors; (ii) poor countries specialize in fewer sectors; (iii) poor countries experience more frequent and more severe aggregate shocks (e.g. from macroeconomic policy); and (iv) poor countries' macroeconomic fluctuations are more highly correlated with the shocks of the sectors they specialize in. We show how to decompose volatility into these four sources, quantify their contribution to aggregate volatility, and study how they relate to the stage of development. We document the following regularities. First, as countries develop, their productive structure moves from more volatile to less volatile sectors. Second, the level of specialization declines with development at early stages, and slowly increases at later stages of development. Third, the volatility of country-specific macroeconomic shocks falls with development. Fourth, the covariance between sector-specific and country-specific shocks does not vary systematically with the level of development. We argue that many theories linking volatility and development are not consistent with these findings and suggest new directions for future theoretical work.

We estimate the impulse response of key US macro series to the monetary policy shocks identified by Romer and Romer (2004), allowing the response to depend flexibly on the state of the business cycle. We find strong evidence that the effects of monetary policy on real and nominal variables are more powerful in expansions than in recessions. The magnitude of the difference is particularly large in durables expenditure and business investment. The effect is not attributable to differences in the response of fiscal variables or the external finance premium. We find some evidence that contractionary policy shocks have more powerful effects than expansionary shocks. But contractionary shocks have not been more common in booms, so this asymmetry cannot explain our main finding. JEL classifications: E52, E32Keywords: asymmetric effects of monetary policy, transmission mechanism, recession, durable goods, local projection methods.

We extend the simulation results given in Santos-Silva and Tenreyro (2006, 'The Log of Gravity', The Review of Economics and Statistics, 88, by considering data generated as a finite mixture of gamma variates. Data generated in this way can naturally have a large proportion of zeros and is fully compatible with constant elasticity models such as the gravity equation All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission in writing of the publisher nor be issued to the public or circulated in any form other than that in which it is published.Requests for permission to reproduce any article or part of the Working Paper should be sent to the editor at the above address.