美国国家公共电台 NPR How Fast Did The Economy Grow? Forecasts Are All Over The Place（在线收听）

RACHEL MARTIN, HOST:

This coming Friday, the U.S. Commerce Department will release a report card on how the U.S. economy is doing. The second quarter gross domestic product, or GDP, is one of the most anticipated numbers this year. It's going to give us an early read on how big of an impact the president's tax cuts are having, for example. This year, though, forecasts for the number are all over the board. NPR's Jim Zarroli reports.

JIM ZARROLI, BYLINE: In the summer of 2008, economists at the New York Federal Reserve Bank saw something disturbing. The statistical model they used to predict where the economy was headed, called the Nowcast, was giving off warning signs. Fed economist Andrea Tambalotti.

ANDREA TAMBALOTTI: All the data turned negative quite quickly and quite abruptly and the Nowcast picked that up. And when you see the Nowcast sort of plunging, then you know that something is wrong.

ZARROLI: What was happening, of course, was the Great Recession, and the Nowcast gave Fed officials a little extra time to prepare for it. The Nowcast was once only released internally, but a couple of years ago, Fed officials began publishing it online.

TAMBALOTTI: We think that it's helpful for the public at large to see these numbers and understand what we do.

ZARROLI: As of this week, the Nowcast is predicting that the U.S. economy grew by a middling 2.7 percent during the second quarter. And then there's the Atlanta Fed's GDPNow. Like the others, it's compiled by crunching a lot of economic data, says Fed economist Pat Higgins.

PAT HIGGINS: So it'll be things like retail sales, international trade, manufacturing shipments.

ZARROLI: And right now, the Atlanta Fed's number is strikingly different than the New York Fed's. It's forecasting a blockbuster GDP of 4 1/2 percent. If you like President Trump's policies, that's the estimate you quote right now. Donald Trump Jr. bragged about the Atlanta Fed numbers on social media, and Treasury Secretary Steve Mnuchin recently trumpeted the Atlanta number on CNBC.

(SOUNDBITE OF CNBC BROADCAST)

STEVEN MNUCHIN: We're expecting a big second quarter GDP number.

ZARROLI: These aren't the only growth estimates being published. Major banks and private firms put out their own numbers. Obviously, all of these numbers can't be accurate, but Andrea Tambalotti says these estimates shouldn't be looked at as competing. Instead, he says, they complement each other.

TAMBALOTTI: We together can have a better sense of, you know, again, is the economy doing well or is the economy not doing so well? Which is what everybody in the end is really interested in.

ZARROLI: Tambalotti says the economy is enormous and ultimately unmeasurable. He says all of these forecasts should be seen as an imperfect baseline. Even the official GDP number released by the Commerce Department is intelligent speculation, and it will be updated as new data comes in, says Pat Higgins.

HIGGINS: The initial numbers are based kind of on incomplete data, so, you know, a year or two from now, you know, the actual estimate could change a lot.

ZARROLI: In fact, the government can come back after a few years and revise the numbers. There have been times when the U.S. economy was actually in recession and no one knew for sure until much later. Still, the GDP report that comes out this Friday is the number that generates headlines and moves markets. Tambalotti calls it the custodian of the true number. And in a sense, that's the only number that matters. Jim Zarroli, NPR News.

[POST-BROADCAST CORRECTION: In the audio of this story, as well as in a previous Web version, we incorrectly say that the New York Federal Reserve Bank had used its Nowcast model to predict the 2008 financial crisis. In fact, the Nowcast was not created until after the Great Recession, but economists later determined that the model would have alerted them to the coming recession had it been used at the time.]

(SOUNDBITE OF MARCUS MILLER'S "DOWN TO THE HEARTH")