That topic has been knocking around for some time, with varying opinions. I’ve now seen the clearest and most thorough treatment to date, namely from Gerald Auten and David Splinter. It hasn’t received that much attention, perhaps because the results don’t have such a strong built-in constituency, but here goes:
Previous studies using U.S. tax return data conclude that the top one percent income share increased substantially since 1960. This study re-estimates the long-term trend in inequality after accounting for changes in the tax base, income sources missing from individual tax returns and changes in marriage rates. This more consistent estimate suggests that top one percent income shares increased by only about a quarter as much as unadjusted shares. Further, accounting for government transfers suggests that top one percent shares increased a tenth as much. These results show that unadjusted tax return based measures present a distorted view of inequality trends, as incomes reported on tax returns are sensitive to changes in tax laws and ignore income sources outside the individual tax system.
You’ll find the paper at the first link here.