February 1, 2005
Seth H. Giertz
This paper applies the methods of Gruber and Saez (2002) to a panel of tax returns spanning 1979 through 2001 in order to examine the sensitivity of the elasticities of taxable and broad income to an array of factors. The paper finds that that Gruber and Saez’s approach yields an estimated elasticity of taxable income (ETI) for the 1990s that is about half the size of this paper’s corresponding estimate for the 1980s. In general, the addition of demographic information has little impact on elasticity estimates for the 1980s, but lowers the 1990s estimates, especially for broad income, which is a more encompassing income measure than is taxable income. Finally, the paper finds that weighting regression results by income not only has a substantial impact on the estimates, but also results in overall estimates that are influenced by a small number of predominately high-income filers. For example, excluding 100 of the most influential observations (just 0.2 percent of the sample) lowers the estimated ETI for the 1980s from 0.37 to 0.11.