By Mike Dunn

PHILADELPHIA (CBS) – Mayor Nutter and City Council intend to implement a new and controversial property assessment system next year, but making it happen isn’t enough, according to a study from the Pew Charitable Trusts.

Getting property assessments correct, so they reflect current market prices for homes, is the stated goal of the mayor’s Actual Value Initiative, or AVI.

But a study from the Pew’s Philadelphia Research Initiative says ramping up AVI in the face of political opposition is only part of the battle.

The author of the report, Emily Dowdall, says keeping those values accurate beyond startup is also a challenge.

“There’s a real danger of property assessments getting inaccurate pretty quickly if they’re not kept up to date,” says Dowdall.

She cites a 2010 study of 14 other Pennsylvania counties that went to full market value programs. Within three years, she says, half of those counties had out of date assessments.

What city council and the mayor need to do, according to the Pew report, is make sure there’s adequate funding for trained staff to conduct regular assessments beyond the startup.

The study can be found at: www.pewtrusts.org.