A housing trade association is examining the possibility that the data it releases underestimated the collapse of the housing industry, the Wall Street Journal reported.

The National Association of Realtors, which issues the monthly existing home sales report that is closely watched by economists and financial markets, may have over-counted home sales dating as far back as 2007, the newspaper said in an article posted to its website.

NAR's home sales count was at odds with calculations by CoreLogic, a California real estate analysis firm, according to the report. CoreLogic says NAR could have overstated home sales by as much as 20 percent.

An over-count of home sales may mean that there is a bigger backlog of unsold homes and that it will take longer for the U.S. housing sector to climb out of the deep hole it is already in, dragging on the broader economic recovery.

The crash of U.S. housing markets, in part because of shoddy lending practices, was at the heart of the economic meltdown that started in the United States and spread around the world.

The U.S. recovery has been held back by the slow healing of housing markets, with high foreclosure rates hold down home values and sales.

NAR said the data could be revised downward this summer, the newspaper said.