Experimental evidence on the effect of taxes

Much of our "fiscal cliff" debate revolves around the incentive effects of raising marginal taxes on high incomes. High tax advocates used to say that taxes won't hurt growth that much, and advocated them for other reasons.  Now they are advocating that even a 91% federal income tax rate, on top of state, sales, etc, as we had in the 1950s, (not counting all the loopholes!) will actually be good for the economy and also raise lots of revenue.

This seems to me like magical thinking, and a great testament to how people can persuade themselves of anything if it suits the partisan passion of the moment.  But wouldn't it be nice if someone would run an experiment for us?

Fortunately, Europe has been running a very useful set of experiments on what happens if you address yawning deficits with high income, wealth and property taxes. Which brings me to a report from the Telegraph

Almost two-thirds of the country’s million-pound earners disappeared from Britain after the introduction of the 50p (percent) top rate of tax, figures have disclosed.

In the 2009-10 tax year, more than 16,000 people declared an annual income of more than £1 million to HM Revenue and Customs.

This number fell to just 6,000 after Gordon Brown introduced the new 50p top rate of income tax shortly before the last general election....

It is believed that rich Britons moved abroad or took steps to avoid paying the new levy by reducing their taxable incomes.

George Osborne, the Chancellor, announced in the Budget earlier this year that the 50p top rate will be reduced to 45p from next April.

Since the announcement, the number of people declaring annual incomes of more than £1 million has risen to 10,000.

However, the number of million-pound earners is still far below the level recorded even at the height of the recession and financial crisis....

Far from raising funds, it actually cost the UK £7 billion in lost tax revenue

That's just one year. Usually, we think that it takes a while for high taxes to have effects. It takes a while for people to move, shelter income, close down businesses, not start businesses, not go to school, etc. Hitting the Laffer limit in one year is pretty impressive.

Update: Thanks to JM Pinder below I went back to the HMRC report which is indeed more detailed. Some highlights:

The 50 per cent additional rate of income tax was introduced on 6 April 2010. It was the first increase in the highest rate of tax in the UK for over 30 years, and was expected to yield around £2.5 billion...

This report provides the first comprehensive ex-post assessment of the additional rate yield using a range of evidence including the 2010-11 Self Assessment returns. The analysis shows that there was a considerable behavioural response to the rate change, including a substantial amount of forestalling: around £16 billion to £18 billion of income is estimated to have been brought forward to 2009-10 to avoid the introduction of the additional rate of tax. ...[This is a suggestion that it's a one time loss. We'll see]
...
The modelling suggests the underlying behavioural response was greater than estimated previously in Budget 2009 and in March Budget 2010, decreasing the pre-behavioural yield by at least 83 per cent. This result is also consistent with that contained in the Mirrlees review, and suggests the additional rate is a highly distortionary form of taxation.

Don't miss the bigger point here. The US discussion harks back to the great old 1950s, ignoring the much more relevant evidence right before us from Europe: Want to try cutting deficits (very slightly) with high marginal taxes, especially on investment, along with minor "cuts" (declines in growth rates) of spending, but no substantial change in the welfare state? Hey, they just tried it! Their economies sink, and they don't get much revenue.