A person with knowledge of the deliberations, who requested anonymity, said the Sept. 28 decision to withdraw the report was made against the advice of the research service’s economics division, and that Mr. Hungerford [the study's author] stood by its findings.What was in the report that terrified Republican Senators so much? In fact, a lot more than reported in the media: "Tax Cuts for the Rich Do Not Spur Economic Growth," Talking Points Memo, September 17; "Tax Cuts for the Rich Cause Income Inequality, Not Economic Growth," Think Progress, September 17; for example.
One major finding is contained in a plot of the top personal income tax rate and real economic growth rates for every year from 1945 to 2010. Contrary to conservative arguments, when the top tax rate was from 70-90+ percent, the country had growth rates averaging 4.2% in the 1950s, but only 1.7% in the 2000s, when the top rate was 35%. Overall, according to Figure 5 of the report, there appears to be no relationship at all between the top tax rate and growth.
It's important to remember, though, that a simple comparison of two variables tells us nothing by itself. It's only when we control for other potential causal factors that we can say whether a relationship does or does not exist between two variables like tax rates and growth. In the report's appendix, the author carries out such a regression analysis, as it's called, and still finds that there is no relationship between the top tax rate and real GDP growth rates.
Moreover, the study takes a look at the ways that lower tax rates are supposed to improve the economy, i.e., by increasing private savings, private investment, and labor productivity growth. In no case does the bivariate analysis (some of which shows higher taxes increasing private savings) or the regression analysis show either the top personal tax rate or the capital gains tax rate having an effect on these intervening drivers of economic growth. This completely undermines the economic arguments for tax cuts as the recipe for a better economy.
But wait, there's more! The diagram (scatterplot) showing the relationship between the top tax rate and the private savings rate shows that the highest private savings rates since 1945 were achieved when the top marginal rate was 70% (see top left of Figure 3), which comports well with recent calculations of the top optimal tax rate (70% or higher). In fact, when the top bracket was 90%, the rate of private savings as a percentage of potential GDP exceeded the rate when it was 40% or below in every year but one!
The other discomfiting finding for the Republican Senators is that lower top tax rates and lower capital gains tax rates increase income inequality. Not only is this obvious in the scatterplots for the top 0.1% and top 0.01%, it remains true in the regression analyses after controlling for other potential causes of the high income shares of the rich.
Tax cuts, then, don't increase economic growth (the ultimate zombie idea, as Paul Krugman says) but do worsen economic inequality. It may even be the case that high top marginal tax rates increase private savings, with the country's historical postwar maximum savings rates coming at a rate of 70%.
What the suppression of this study amounts to, then, is part of the present-day Republican Party's war on science, arithmetic, and knowledge in general. Unable to refute the findings of the CRS report, they demand its censorship instead. As Jared Bernstein says, this is simply scary: "this type of suppression is wholly inconsistent with democracy." That Congress' non-partisan research arm is going along with this makes it especially chilling.