As anyone who writes or collects a rent check each month knows, rent regulations are a matter of numbers.

This year, as both landlords and tenants argue about the state’s rent laws — which expire in June — they look to hard numbers to make their case.

For tenant advocates, housing data recently released by the city, when compared to figures from three years ago, could put a wrench in their campaign.

That is, if the data were actually correct.

When the city’s lead housing analyst, Dr. Moon Wha Lee, released the results of the city’s triennial Housing and Vacancy Survey on February 7, he urged readers not to jump to conclusions based on the numbers, since they were still incomplete.

Whoops. Despite a huge math problem that should stop anyone from comparing the city’s 1999 and 2002 surveys, at least one city Housing Preservation and Development official and a landlord lobbyist have been using flawed numbers to make their case in the state’s upcoming debate on rent regulation.

This year’s rent debate in Albany is focusing on “vacancy decontrol,” a 1993 amendment — expanded in 1997 — that lets landlords remove an apartment from the rent stabilization program once the rent hits $2,000. Tenant advocates want decontrol repealed. New York State Tenants and Neighbors estimates it has deregulated 99,000 apartments.

Some city officials and landlord advocates, however, are tossing around an entirely different set of numbers. At a state assembly hearing on February 12, HPD Deputy Commissioner Joseph Rosenberg told Assemblymember Vito Lopez that he didn’t agree with Tenants and Neighbors’ estimate, saying “We don’t believe it’s anywhere near [99,000].” In fact, Rosenberg continued, HPD’s 2002 housing survey showed an increase of 21,000 rent stabilized units since 1999, to 1.065 million.

Hold on, says Lee, an HPD assistant commissioner. “It’s inappropriate to compare the 2002 numbers to 1999,” he told City Limits. Here’s why: The 2002 housing survey was based on addresses obtained by the 2000 census, while the 1999 housing survey was based on the 1990 census. Because the 2000 census was more accurate than 1990’s, roughly 370,000 new addresses turned up citywide. The 2002 survey is based on that larger number of housing units.

To make things clearer, Lee says HPD will “reweight” all of its 1999 numbers within a few months and release final 1999 and 2002 numbers that can actually be compared.

In the meantime, the preliminary — and flawed — numbers are entering the contentious rent regulation debate. Later during the February 12 hearing, landlord advocate Dan Margulies, of the Community Housing Improvement Program, echoed Rosenberg’s claim that the number of regulated units may have increased.

That infuriates Michael McKee, associate director of Tenants and Neighbors. “It’s totally disingenuous for HPD-or anyone else-to say there’s more regulated units than three years ago,” McKee says. While affordable housing construction and rehab programs do add some new units to rent stabilization, Tenants and Neighbors says that number is dwarfed by those apartments that have been deregulated.

HPD is now backing off Rosenberg’s testimony, claiming that the deputy commissioner did say his numbers were preliminary. The agency admits that it really doesn’t know what the final numbers will show. “We just don’t have the right data yet,” says HPD spokesperson Virginia Gliedman. “We’re just salivating to do the proper analysis.”