An apparent mistake in San Diego home sales figures reported by the nonprofit Sandicor to the California Association of Realtors vastly overestimated the number of sales going back several months.

For instance, instead of a reported 89.1 percent increase in year-over-year existing home sales in May, the increase was actually 6.5 percent. Instead of a 63 percent increase year-over-year home sales in April, the increase was actually 20 percent.

Robert Kleinhenz, deputy chief economist of the California Association of Realtors, said the group plans to issue revised numbers July 27. The revisions could go as far back as spring 2008.

Sandicor CEO Ray Ewing said July 2 the glitch appears to be human error that began when Sandicor upgraded its MLS system around late August 2008. Prior to the upgrade, Sandicor had been sending one home sales report to the National Association of Realtors, which included pending home sales, and a separate report to the California Association of Realtors, which did not include pending home sales. After the upgrade, Sandicor began sending CAR the same report it sent to NAR.

“I believe what happened was we gave them something that wasn't seen in the past,” said Ewing, who said the numbers may be off from September 2008 until now. “I can understand the error. We introduced the new number to CAR. Our assumption was they would ignore it.”

Instead it appears that CAR counted pending home sales with final sales, Ewing said.

Kleinhenz said the glitch wasn’t identified until last week when an East Coast real estate analyst, Thomas Lawler, pointed out in a newsletter the discrepancies between the California association’s numbers and those reported by MDA Dataquick of La Jolla, as well as his own numbers.

Kleinzhenz said one of the reasons the mistake went undetected for so long is that in some California markets, there were more than 100 percent gains.

“An 89 percent gain in sales doesn’t seem all that implausible because over the last several months many areas had huge gains in sales — from 50 percent to 100 percent, and some areas had 200 percent gains year-over-year,” Kleinhenz said. “Eighty-nine percent looks like a large number compared to 6.5 percent, but it’s not all that implausible. It fit into the ballpark of what we were seeing.”

Kleinhenz said the mistakes are not consistent throughout the year.

“And some points in time the information may have included the pendings, and at other times it did not. We’ll have to go back and revise the entire series,” he said.

He said the MLS is more designed for listing information rather than tracking it.

“It’s kind of an art to figure out how to pull right the line-by-line information that can be used in our reports,” Kleinhenz said.