Data on sales of previously owned U.S. homes from 2007 through October this year will be revised down next week because of double counting, indicating a much weaker housing market than previously thought.
The National Association of Realtors said a benchmarking exercise had revealed that some properties were listed more than once and in some instances new home sales were also captured.
"All the sales and inventory data that has been reported since January 2007 is being downwardly revised. Sales were weaker than people thought," NAR spokesman Walter Malony told Reuters.
"We're capturing some new home data that should have been filtered out and we also discovered that some properties were being listed in more than one list."
The benchmark revisions will be published next Wednesday and will not affect house prices.
Early this year, the Realtors group was accused of overcounting existing homes sales, with California-based real estate analysis firm CoreLogic claiming sales could have been overstated by as much as 20 percent.
At the time, the NAR said it was consulting with a range of experts to determine whether there was a drift in its monthly existing home sales data and that any drift would be "relatively minor."
The depressed housing market is one of the key obstacles to strong economic growth and an oversupply of unsold homes on the market continues to stifle the sector.
Malony said the Realtors group had developed a new model that would allow frequent benchmarking instead of waiting 10 years for the population Census data to revise their figures.