Tax Math

Higher taxes are most likely in our future, regardless of who we elect:

Douglas Holtz-Eakin, a former Director of the Congressional Budget Office and current chief McCain economic advisor, is an honest man--which means he's something of a liability on the Straight Talk Express. A few months ago, he admitted to my colleague, Michael Scherer, that Barack Obama's economic plan would reduce taxes for most people. And now, in a forthcoming book by Fortune columnist Matt Miller, he makes it clear that the next President is going to have to raise taxes.

"If you do nothing on the spending side, you're going to have to raise taxes whether you're a Republican, a Democrat or a Martian," he tells Miller...and then he immediately makes it clear that the "spending side" part of the argument is nothing more than a political fig-leaf.

And the futures market is also betting on rising taxes according to Mankiw.

The top income tax rate is now 35 percent. According to the betting at Intrade, the probability that the top income tax rate in 2011 will exceed 38 percent is 0.87. Call this P(tax hike).

Barack Obama has made such a tax hike part of his campaign promises, and there is no reason to think the Congress won't deliver for him. So let's assume Obama is certain to get the tax hike if he wins. That is, P(tax hike / Obama) = 1.0. (If this assumption is wrong, and this conditional probability is less than one, then my conclusion below would be even stronger.)

According to Intrade, the probability of Obama being the next president is 0.53. Call this P(Obama). And P(McCain) = 0.47.

Now we can calculate the probability of a tax hike conditional on McCain winning. It comes from the formula

P(tax hike)
= P(tax hike/Obama) P(Obama) + P(tax hike/McCain) P(McCain),

and plugging in the above numbers. It tells us that

P(tax hike / McCain) = 0.74.