Would a significant increase in the top (US) marginal income tax rate substantially alter income inequality?
This, you might think, qualifies as another in the series “Short Answers to Silly Questions”. But a Brookings Paper study by William G. Gale, Melissa S. Kearney, and Peter R. Orszag reaches the opposite conclusion. (Hat tip: Harry Clarke).
The study looks at increasing the top marginal tax rate (currently 39.6, applicable to incomes above $400k for singles), with the strongest option being an increase to 50 per cent. The proceeds are assumed to be redistributed to households in the bottom 20 per cent of the income distribution.
The headline finding is that the Gini coefficient is barely changed, as are other popular measures including the 99/50 ratio (the ratio of income at the 99-th percentile to 50-th percentile, that is the median). But the 99/10 ratio and 90/10 ratios change a lot, from 50 and 17 under current law to 37 and 12.5 with the redistribution.
What does this mean? Two things:
(i) As is well known, the Gini coefficient is a lousy measure of income inequality, much more sensitive to the middle of the income distribution than to the tails
(ii) The proposed redistribution would substantially improve the welfare of the poor, with most of the burden being borne by taxpayers in or near the top 0.1 per cent.
It’s obvious, as the authors note, that the 90-50 measure won’t change, since neither group is affected (there’s no simulation of behavioral responses which might have indirect effects). But, since the 99-th percentile income is very close to $400k, there’s very little impact on this group either. But the tax, as modelled, raises a lot of money from the ultra-rich incomes. As a result, distributing the proceeds at the bottom of the distribution raises incomes substantially, which explains the big changes in the 90-10 and 99-10 ratios.
The real lesson to be learned here, one I came to pretty slowly myself is that old-style measures looking at quintiles or even percentiles of the income distribution are no longer very relevant. The real question, in the economy of Capital in the 21st Century is how much should go to the ultra-rich.