Existing-home sales were up in November, but down for the last five years compared to what estimates had previously stated, according to the National Association of Realtors (NAR), which today released revisions to its sales and inventory data dating back to 2007.

The NAR has been reviewing its data since early this year, when its estimates were called into question by CoreLogic, a Santa Ana, Calif.–based analytics firm, and the Mortgage Bankers Association. They contended that the NAR’s numbers were overstating sales by between 15% and 20%.

In the numbers released today, the NAR downwardly revised total sales and inventory estimates for 2007 through 2010 by 14.3%. For 2010 alone, existing-home sales were revised down 14.6% to 4,190,000, from the previously projected 4,908,000.

October 2011’s annual estimate was revised down 14.5% to 4.25 million, from 4.97 million.

Numbers of existing homes on the market were also moved downward. Overall, inventory was revised down 14.3%; October 2011’s inventory stock was revised down 18% to 2.74 million.

The NAR attributed the need for revision to a divergence between MLS data and sales numbers from the U.S. Census benchmark. The variance, the NAR said in a release today, began in 2007 and stemmed from growth in MLS coverage areas and population shifts. About half the revisions were the result of a decline in for-sale-by-owner (FSBO) transactions, as more home sellers turned to Realtors to market their properties when the market softened, the NAR said.

"The FSBO market was overwhelmed during the housing downturn, and since most FSBOs are not reported in MLSs, national estimates of existing-home sales began to diverge based on previous assumptions," said Lawrence Yun, the NAR’s chief economist, in a statement today. "In addition to a decline in FSBO transactions, more builders began marketing new properties through real estate brokers that weren’t completely filtered from the existing-home data. Some property listings on more than one MLS and issues related to house filing also contributed to the downward revisions."

But while the NAR’s historic numbers were falling, more recent estimates have been on the way up. Overall, existing-home sales increased 4.0% in November to reach a seasonally adjusted annual rate of 4.42 million units.

The bump came from single-family homes, which saw sales increase 4.5% for the month, while condo and co-op sales remained unchanged.

On an annual basis, sales were up 12.2%. However, that improvement came at the cost of prices: In November both median and average prices stood 3.5% lower than a year earlier. Much of the devaluation has come from distressed sales, which inched up in November to 29% of transactions, from 28% in October.

Inventory was also slightly down in November, according to the NAR, which reported it slipped seven-tenths of a point to a seven-month supply. The number of Realtors reporting contract failures was unchanged from October at 33%.

Claire Easley is a senior editor at Builder.