The Bureau of Economic Analysis reported the following on July 28:
Real gross domestic product... increased at an annual rate of 2.5 percent in the second quarter of 2006... In the first quarter, real GDP increased 5.6 percent.
Ouch; sounds like the economy slowed down, doesn’t it?
Don’t believe it just yet. In my view, real growth didn’t drop, it increased. I’ll explain below, but for now, here’s how I would have reported the Q2 results:
Based on Q1&2 2006 results, real GDP increased at an annual rate of 4.0%. That compares with the Q4&1 result of 3.6% reported last month. The real GDP growth rate increased.
Explanation
To calculate the growth rate, the BEA annualizes the one-quarter change in GDP. But an alternative way of calculating it is to annualize the two-quarter change. I’ve been doing that calculation for a year, then posting the result here each month. Here's the latest result:
[UPDATE: Click here for a brief, explicit summary of the math.]
Why do I calculate it two different ways? Because the two-quarter method has been a better predictor than the one-quarter method has been. I’ve back-tested both methods, quarter-by-quarter, from 1970 to now. Result: The “annual growth rate” from the 2-qtr method is still a better predictor of GDP four quarters into the future. It has won 58% of the time since 1970, 58% of the time since 1980, and 60% of the time since 1990. (In an election, 60% would be a “landslide.”)
The 2-qtr method yields a growth rate that changes more smoothly quarter-to-quarter; the 1-qtr method is a lot jerkier. [Important note: The BEA is not in the forecasting business; they are working hard to report what did happen, not what will happen, and they are doing an excellent job of it. The 1-qtr method says the economy grew at an annual pace of 2.5% in Q2. Although it’s also a fact that the 2-qtr method yields 4.0%, the BEA only reports the results of the 1-qtr method.]
Below is a recap of the two methods, going back several quarters.
If you’re interested in a more-detailed comparison, click on the thumbnail immediately below. It’s the simplest way I could think of to show how accurate the two methods are, when used to forecast GDP four quarters into the future. Email me if you have a question about it.
Bottom line
Contrary to conventional wisdom, real GDP growth appears (to me) to be accelerating. If that upsets, or confirms, anyone’s political agenda... well, sorry, but it’s purely an accident. I do have some private-sector forecasting experience, and I always prefer the method that yields the more reliable prediction, no matter whose pet theory is affected. In this case, the 2-qtr method has been the more reliable predictor. Real GDP is growing closer to a 4.0% rate than 2.5%.

We can indeed “cure” our trade deficit problems if we can create enough unemployment and hard times at home.
Every time I read an article that mentions the deficit or the debt, I can count on reading—one more time—the sob-story cliché about how our “children and grandchildren” will have to pay “higher taxes” because of those deficits we’re running today.
I'm reading a book I will soon be recommending to everyone who's interested in plain-talk discussions of economics – growth economics, to be more specific. The title of the article will be "Yes, there is a free lunch." I'll finish reading the book before I write the article, but if you'd like to get a jump on it, the name of the book is Knowledge and the Wealth of Nations, by David Warsh (2006). The first half is about economic history; the second half is about Paul Romer's shakeup of economic history, beginning in 1990, still under way. (See "Now Reading" in the right-hand column of this blog.)
Growth is a form of change. Change implies innovation; and the Western system of innovation has depended upon wide diffusion of the power to undertake and use innovations, coupled with ample rewards for success and penalties for failure.
A scary article was just published a few days ago, titled Is the United States Bankrupt? But it wasn’t the title that was scary to me; let’s face it, we see that title all the time, because it’s a sure-fire grabber that sells newspapers, magazines, and books, lickety-split. As I recall, the last time I saw that title was six or seven weeks ago in the grocery store checkout line... but I just can’t remember if it was gracing the front page of the Globe, the Weekly World News, or the National Enquirer.
Unlike most forms of geometric expansion, there is no reason to believe that the expansion of knowledge has any inherent limits.