Alwyn Young - Research

Stata Code

Randomization confidence intervals for OLS regression models: randcmdci.ado & randcmdci.sthlp. Randomization-t confidence intervals and p-values that are asymptotically robust to deviations from the sharp null in favour of average treatment effects.

Randomization inference p-values (updated 5/2020): randcmd.ado & randcmd.sthlp (also available through ssc install in Stata). Randomization-c and -t p-values for individual treatment effects and joint Wald and Westfall-Young multiple-testing tests of statistical significance for equations with multiple treatment effects and for an experiment as a whole. The omnibus test (available in earlier versions) has been restored at the request of users.

Effective degrees of freedom corrections (updated 10/2016): edfreg.ado & edfreg.sthlp, The updated version runs faster and allows for absorbed fixed effects, weights and noconstant.

Working Papers

"Asymptotically Robust Randomization Confidence Intervals for Parametric OLS Regression." September 2020. On-line appendix.

Merging results concerning the asymptotic distribution of permutation statistics with White's (1980) proof of the asymptotic accuracy of heteroskedasticity robust inference, this paper shows that insofar as conventional inference asymptotically provides accurate coverage probabilities, randomization tests using sharp nulls that incorrectly specify an absence of heterogeneity do so as well, regardless of covariate interactions or the level of standard error clustering. Intuitively, in all cases the distribution of the Wald statistic across permutations of treatment converges to that of a chi-squared variable. When the conventional test statistic is similarly asymptotically distributed chi-squared, the order statistics of the permutation distribution average the linearly accurate coverage probabilities of the conventional test. The additional to White (1980) assumptions used to prove the result are that treatment is iid, interactions are included separately as covariates, sufficiently high moments of treatment, interactions and errors exist, and the maximum size of interdependent observations is bounded.

"Misspecified Politics and the Recurrence of Populism." (joint with Gilat Levy and Ronny Razin). January 2021. On-line appendix.

We develop a model of political competition between two groups that differ in their subjective model of the data generating process for a common outcome. One group has a simpler model than the other group as they ignore some relevant policy variables. We show that perpetual changes of power are a natural feature of this dynamic learning environment and that simple world views - which can be interpreted as populist world views - imply extreme policy choices. Periods in which those with a more complex model govern increase the specification error of the simpler world view, leading the latter to underrate the effectiveness of complex policies and overestimate the positive impact of a few extreme policy actions. Periods in which the group with the simple world view implement their narrow policies result in subpar outcomes and a weakening of their omitted variable bias. Policy cycles arise, where each group's tenure in power sows the seeds of its eventual electoral defeat.

“Consistency Without Inference: Instrumental Variables in Practical Application.” February 2020. Appendix.

I use Monte Carlo simulations, the jackknife and multiple forms of the bootstrap to study a comprehensive sample of 1359 instrumental variables regressions in 31 papers published in the journals of the American Economic Association. Monte Carlo simulations based upon published regressions show that non-iid error processes in highly leveraged regressions, both prominent features of published work, adversely affect the size and power of IV estimates, while increasing the bias of IV relative to OLS. Weak instrument pre-tests based upon F-statistics are found to be largely uninformative of both size and bias. In published papers, statistically significant IV results generally depend upon only one or two observations or clusters, IV has little power as, despite producing substantively different estimates, it rarely rejects the OLS point estimate or the null that OLS is unbiased, while the statistical significance of excluded instruments is substantially exaggerated.

“Improved, Nearly Exact, Statistical Inference with Robust and Clustered Covariance Matrices using Effective Degrees of Freedom Corrections.” January 2016.

I propose bias and effective degrees of freedom corrections, based upon mimicking the first two moment properties of a chi-squared variable, to statistical inference using robust and clustered covariance matrices. Simulation, using 1378 practical regression examples found in 44 experimental papers, shows that these corrections render the test statistics nearly exact in the face of ideal iid normal errors and provide large improvements in the accuracy of statistical inference in the presence of distinctly non-iid non-normal errors.

Published Papers by Topic

Applied Econometrics

"Channelling Fisher: Randomization Tests and the Statistical Insignificance of Seemingly Significant Experimental Results." Quarterly Journal of Economics 134 (May 2019): 557-598. Preprint. Appendix.

Macroeconomic Implications of Worker Self Selection

"Structural Transformation, the Mismeasurement of Productivity Growth, and the Cost Disease of Services." American Economic Review 104 (November 2014): 3635-67.

Files: Appendix.. US sectoral TFP growth.  Data and programmes.

"Inequality, the Urban-Rural Gap, and Migration." Quarterly Journal of Economics 128 (November 2013): 1727-1785. Preprint. Appendix. DHS based migration data.

The Aids Epidemic and African Growth

"The African Growth Miracle." Journal of Political Economy 120 (August 2012): 696-739.  Data and programmes.

"In Sorrow to Bring Forth Children: Fertility amidst the Plague of HIV." Journal of Economic Growth 12 (December 2007): 283-327.

“The Gift of the Dying: The Tragedy of AIDS and the Welfare of Future African Generations.” Quarterly Journal of Economics 120 (May 2005): 423-466.

Growth and Reform in the People's Republic of China

“Gold into Base Metals: Productivity Growth in the People’s Republic of China during the Reform Period.” Journal of Political Economy 111 (December 2003): 1220-1261.

“The Razor’s Edge: Distortions and Incremental Reform in the People’s Republic of China.” Quarterly Journal of Economics 115 (November 2000): 1091-1135.

East Asian Productivity Growth

“The Tyranny of Numbers: Confronting the Statistical Realities of the East Asian Growth Experience.” Quarterly Journal of Economics 110 (August 1995): 641-680.

“Lessons from the East Asian NICs: A Contrarian View.” European Economic Review 38 (1994): 964-973.

“A Tale of Two Cities: Factor Accumulation and Technical Change in Hong Kong and Singapore.” In NBER, Macroeconomics Annual 1992. Cambridge, MA: MIT Press, 1992. 

Models of Endogenous Growth

“Growth without Scale Effects.” Journal of Political Economy 106 (February 1998): 41-63.

“Substitution and Complementarity in Endogenous Innovation.” Quarterly Journal of Economics 108 (August 1993): 775-807.

“Invention and Bounded Learning by Doing.” Journal of Political Economy 101 (June 1993): 443-472.

“Learning by Doing and the Dynamic Effects of International Trade.” Quarterly Journal of Economics 106 (May 1991): 369-405.

Ballistic Missile Defense

“Ballistic Missile Defense: Capabilities and Constraints.” The Fletcher Forum 8 (Winter 1984).

Reprinted in Department of Defense, Current News, Special Edition, No. 1142, 25 April 1984 and Air War College, Strategic Nuclear Force Posture, Vol. II, Chap. 5, December 1984.

Resting Papers

"The Gini Coefficient for a Mixture of Ln-Normal Populations."  December 2011.  (Data and programmes).

“Demographic Fluctuations, Generational Welfare and Intergenerational Transfers.” October 2001.

“Transport, Processing and Information: Value Added and the Circuitous Movement of Goods.” May 1999.