In a column for the NY Times, he uses himself as an example of how a change in marginal tax rates could reduce labor supply:
Suppose that some editor offered me $1,000 to write an article. If there were no taxes of any kind, this $1,000 of income would translate into $1,000 in extra saving. If I invested it in the stock of a company that earned, say, 8 percent a year on its capital, then 30 years from now, when I pass on, my children would inherit about $10,000. That is simply the miracle of compounding.So, if Mankiw's marginal tax rate reverts to its Clinton-era levels as scheduled under current law, when his editor calls to tell him its time for a new edition of his textbook, he would decline?
Now let’s put taxes into the calculus. First, assuming that the Bush tax cuts expire, I would pay 39.6 percent in federal income taxes on that extra income. Beyond that, the phaseout of deductions adds 1.2 percentage points to my effective marginal tax rate. I also pay Medicare tax, which the recent health care bill is raising to 3.8 percent, starting in 2013. And in Massachusetts, I pay 5.3 percent in state income taxes, part of which I get back as a federal deduction. Putting all those taxes together, that $1,000 of pretax income becomes only $523 of saving.
And that saving no longer earns 8 percent. First, the corporation in which I have invested pays a 35 percent corporate tax on its earnings. So I get only 5.2 percent in dividends and capital gains. Then, on that income, I pay taxes at the federal and state level. As a result, I earn about 4 percent after taxes, and the $523 in saving grows to $1,700 after 30 years.
Then, when my children inherit the money, the estate tax will kick in. The marginal estate tax rate is scheduled to go as high as 55 percent next year, but Congress may reduce it a bit. Most likely, when that $1,700 enters my estate, my kids will get, at most, $1,000 of it.
HERE’S the bottom line: Without any taxes, accepting that editor’s assignment would have yielded my children an extra $10,000. With taxes, it yields only $1,000. In effect, once the entire tax system is taken into account, my family’s marginal tax rate is about 90 percent. Is it any wonder that I turn down most of the money-making opportunities I am offered?
By contrast, without the tax increases advocated by the Obama administration, the numbers would look quite different. I would face a lower income tax rate, a lower Medicare tax rate, and no deduction phaseout or estate tax. Taking that writing assignment would yield my kids about $2,000. I would have twice the incentive to keep working.
If we're doing a social cost-benefit analysis of changing Greg Mankiw's marginal taxes, we should account for externalities, positive and negative. Following Mankiw's lead, I'll use myself as an example, and explain a benefit to reducing Mankiw's labor supply that should be accounted for in his analysis.
I would be better off if he decided the marginal benefit of an cranking out eighth edition was less than the marginal cost, and so would my students. The churning of textbook editions (and this isn't Mankiw's fault, to be sure) is a real headache to instructors, and helps keep the cost high for students. Though I'm sure it was well-intentioned (and thoroughly focus-grouped) a number of the changes from the sixth to seventh edition of his textbook made it worse from my point of view. For example, I rather liked his discussion of New Keynesian and Real Business Cycle theory, which were supplanted by a "dynamic aggregate demand and supply" chapter that I'm not inclined to mess with. And don't tell me I need my book "updated" for "current events." One of the fun things about teaching macroeconomics is that the world is always giving us interesting new examples to talk about. But I can handle that quite well without some new "economics in the news" sidebars grafted into the textbook.
However, while the theoretical case that marginal tax rates can change behavior is clear, I'm not convinced, as an empirical matter, that Mankiw's would actually change. After all, his book was first published in 1992, and he issued new editions in 1994 and 1997 when higher marginal tax rates on high levels of income (and capital gains and estates) were in effect.
Mark Thoma and Brad DeLong suggest some other possible shortcomings in his argument.