Taxable Income Responses to 1990s Tax Acts: Further Explorations

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. In general, estimates are quite sensitive to a number of different factors. In contrast to some of the literature, estimates are larger when behavior is measured over three-year intervals as opposed to over one-year intervals – suggesting small transitory responses to tax changes, but larger longer-term responses. When including the richest set of income controls, income-weighted elasticity estimates based on one year differencing range from 0 to 0.19. Similarly estimated elasticities over three year intervals are about 0.32. When adding adjacent year tax rates to model, estimates based on one year differencing now range from 0.30 to 0.43 and estimates when differencing over three year intervals range from 0.97 to 1.37. In most cases, estimates from an end-year approach are not statistically different from 0 for the 1990s. However, even for the approaches that produce statistically significant results, estimates are sensitive to an array of factors and plausible sensitivity checks often result in estimates that differ greatly. A major conclusion is that isolating the true taxable income responses to tax changes is inherently complex and little confidence should be placed on any single estimate.