BILLINGS, Mont.  — A new study concludes that a multimillion-dollar advertising campaign to deter youths from trying methamphetamines has failed to speed up a longstanding decline in the drug’s use.

Economics researcher D. Mark Anderson of the University of Washington said Tuesday that abuse of the drug already was on the decline before the high-profile Montana Meth Project began in 2005.

An estimated $13 million has been spent on the Montana campaign, and identical programs have since been launched in seven other states: Arizona, Idaho, Illinois, Wyoming, Colorado, Hawaii and Georgia.

Using billboards and other advertisements that link meth abuse to teen prostitution, crime and death, the project has been touted as an unqualified success by many politicians and law enforcement officials.

But Anderson’s study, in the September issue of the Journal of Health Economics, calls into question whether that advertising money is being well spent.

Anderson compared Montana meth usage trends between 1999 and 2009 with trends in neighboring states and the nation.

“When I control for the fact that meth has not only been decreasing in Montana over a long time period but also pretty much everywhere else, I find no effect from the project,” he said.

Montana Meth Project director Bill Slaughter faulted Anderson’s conclusions and said it did not reflect that the rate of meth decline accelerated after the campaign was launched.

Between 1999 and 2005, the number of youths reporting they had used meth fell 39 percent. Between 2005 and 2009, the drop was 63 percent, Slaughter said.

“(Anderson) takes a couple of points of comparison and concludes the meth project has not had an impression,” he said.

However, a closer examination of the numbers reveals that the change in rate was largely a function of the number of youths taking meth: As that number got lower, the same pace of decline yielded a larger percentage figure in terms of the rate. But the actual change was identical in both time periods.

From 1999 to 2005, the percentage of Montana youths who used meth in their lifetime fell from 13.5 percent to 8.3 percent — a 5.2 percent change. From 2005 to 2009, it fell to 3.1 percent — another 5.2 percent change.

Anderson said he used the same data referenced by Slaughter to reach his conclusions, the biennial Youth Risk Behavior Survey from the Centers for Disease Control and Prevention.

The strides in prevention touted by the Meth Project’s supporters, he said, does not stand up from a statistical standpoint.

“If I had found the meth project had an effect, that’s what would have been reported,” he said. “I just wanted to know if this anti-drug campaign worked and I found that it didn’t.”

Similar concerns have been raised about a drug prevention program that began in the 1980s, Drug Abuse Resistance and Education. Also known as DARE, it is employed by schools across the country despite multiple studies over the past two decades that said it yielded little or no benefit.

The findings on the Montana Meth Project also are in line with conclusions reached in 2008 by an Australian researcher.

David Erceg-Hurn, a doctoral candidate in clinical psychology at the University of Western Australia, contended that the Meth Project’s reports distorted the program’s successes by emphasizing positive numbers.

He concluded that after six months of exposure to the ads, there was an increase in the percentage of teens who said using methamphetamine was not a risky behavior or who strongly approved of regular meth use.