Institute on Taxation and Economic Policy. May 29, 2009.
Where Have All of Maryland's Millionaires Gone? finds that Maryland's 2007 and 2008 tax hikes on the rich did not cause millionaires to flee. Although tax returns filed by millionaires declined in the year after the legislation passed, the culprit wasn’t rising taxes, it was the economic downturn.
The decline in millionaire tax filer more likely related to the fact that, at least for 2008, there were fewer millionaires in Maryland due to the onset of the Great Recession. If the reduction in millionaires directly related to the tax hikes, presumably we would have seen migratory trends among all income groups affected by the tax hikes, but while individuals/families with incomes above $150,000/$200,000 also had their state taxes raised, the number of returns in that tax bracket actually rose (at least in part because of the ex-millionaires bolstering their ranks?).
