A housing trade association is examining the possibility 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 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 on its web site.

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 US housing sector to climb out of the deep hole it is already in, dragging on the broader economic recovery.