"Q1 GDP growth tends to be the lowest of the four quarters," said Tom Stark, manager of the Real-Time Data Research Center at the Federal Reserve Bank of Philadelphia. Stark was one of three economists who duplicated CNBC's results. He said that statistically, "the results seem fairly robust over a number of alternative samples."
Officials at the Bureau of Economic Analysis, which tabulates and compiles the GDP data, initially declined to comment to CNBC. But after the story was published, Brent Moulton, associate director for national economic accounts, said even though the data is adjusted for seasonal patterns, it can still show so-called "residual seasonality."
"BEA is currently examining possible residual seasonality in several series, which may lead to improvements in....the regular annual revision to GDP scheduled for July," he added.
"I find it odd," said UBS economist Drew Matus, whose own work confirmed the CNBC findings. The data, over the three-decade time span, "should have corrected or been corrected." He added, "We have to be cautious in reading too much into data and/or delaying policy because of data that exhibits a bias over long periods of time."
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Wall Street seems unaware of the phenomenon, or at least does not appear able to anticipate the Q1 effect in its forecasts. An analysis of separate data by CNBC shows that Wall Street has underestimated Q1 GDP 80 percent of the time since 1985, the most for any quarter and with often substantial misses.
The implications for policymakers and investors are potentially significant. CNBC's Rapid Update, a running average of GDP forecasts, shows the first quarter tracking at only 1.2 percent, a full point below the fourth quarter. As the Federal Reserve considers its first interest rate hike in nearly a decade, some Fed officials have said the recent weak economic data give them pause.
The reason for under-performance in the first quarter is ultimately unclear. GDP totals the value of all of the nation's production and is revised multiple times over years. It is seen as a less-than-perfect measure. Data are seasonally adjusted by individual category while the number as a whole is not. It could be that some events that happen fairly regularly in the first quarter—such as really severe weather or declines in defense or business spending—don't happen quite regularly enough to be picked up by seasonal adjustments.
First quarter data since 2010 has been especially depressed, averaging a paltry 0.62 percent while the economy grew 2.3 percent. Those are numbers more like Europe since the recession, not the U.S. The average is heavily affected by two quarters of negative growth, including a 2.1 percent decline last year. That decline was blamed on harsh weather across the nation, but economists still had trouble explaining its recession-like severity, coming after two quarters of strong growth and preceding two quarters of even stronger numbers.
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And while economists could look out their window and see the lousy weather, they couldn't predict the plunge in GDP in the first quarter of 2014 to minus 2.1 percent: The consensus estimate looked for a positive 1.1 percent, but that was a whopping miss of 3.2 percentage points. The Street was even worse in 2011, looking for 1.9 percent growth in the first quarter compared to minus 1.5 percent.