February 2, 2006
Seth H. Giertz
This paper examines alternative methodologies for measuring responses to the 1990 and 1993 federal tax increases. The methodologies build on those employed by Gruber and Saez (2002), Carroll (1998), and Auten and Carroll (1999). Internal Revenue Service tax return data for the project are from the Statistics of Income, which heavily oversamples high-income filers. Special attention is paid to the importance of sample income restrictions and methodology. Estimates are broken down by income group to measure how responses to tax changes vary by income. In general, estimates are quite sensitive to a number of different factors. Using an approach similar to Carroll’s yields elasticity of taxable income (ETI) estimates as high as 0.54 and as low as 0.03, depending on the income threshold for inclusion into the sample. Gruber and Saez’s preferred specification yields estimates for the 1990s of between 0.20 and 0.30. Yet another approach compares behavior in a year before a tax change to behavior in a year after the tax change. That approach yields estimated ETIs ranging from 0 to 0.71. The results suggest tremendous variation across income groups, with people at the top of the income distribution showing the greatest responsiveness. In fact, the estimates suggest that the ETI could be as high as 1.2 for those at the very top of the income distribution. The major conclusion, however, is that isolating the true taxable income responses to tax changes is extremely complicated by a myriad of other factors and thus little confidence should be placed on any single estimate. Additionally, focusing on particular components of taxable income might yield more insight.