Washington • National home sales figures will be lowered dating back to 2007 after the private trade group that collects them said the numbers were too high.

The National Association of Realtors said Monday it will release the downward revisions for previously occupied homes on Dec. 21.

Among the reasons for the inflated figures, the Realtors group says were changes in the way the Census Bureau collects data, population shifts and some sales being counted twice. Last year's total sales figure of 4.91 million was the worst in 13 years.

The Realtors consulted with several government and private housing market experts, including the Federal Reserve, the Department of Housing and Urban Development, the Mortgage Bankers Association, the National Association of Home Builders, mortgage giants Fannie Mae and Freddie Mac, and CoreLogic, the California-based data firm that first raised doubts about the annual numbers earlier this year.

CoreLogic estimated that the Realtors group overstated sales in 2010 by at least 15 percent.

The changing numbers could impact how economists view data from the trade group. It could also affect companies who use the figures for hiring and expansion plans.