National Association of Realtors overstated existing home sales by 16.7%

Last week I blogged about the National Association of Realtors overstating existing homes sales over the past five years. At the time we didn't know how much the Realtors overstated the numbers. Now we know they overstated them by 16.7%:

Existing home sales during the housing bust were actually 14.3% worse than previously reported, a revision to Realtors' group numbers shows.

On Wednesday, the National Association of Realtors (NAR) revised home sale counts back to 2007 due to flaws in their original data analysis.

In 2007, there were actually just 5.04 million existing home sales, 11% less than the 5.65 million originally reported. Even worse were 2008 and 2009, when there were 16% fewer sales than originally reported. Sales in 2010 were 15% lower.

"The errors started in 2007 and continued to accumulate over time," said Lawrence Yun, NAR's chief economist. ...

The data is "key to the economic outlook," said Mark Zandi of Moody's Analytics, "and the revisions help to explain the severity of the housing crash." ...

Some industry sources had been critical of the organization's data. In February, CoreLogic charged that NAR data was overestimating sales by 15% to 20%.

When NAR investigated, it found a "notable upward drift" in the numbers compared to other measurements such as courthouse deeds records, said Yun.

For anyone confused about where the 16.7% in the title comes from, the first sentence of the quoted article says sales were 14.3% worse than previously reported, and 100 / (100-14.3) = 16.7.