A reasonable worry with the rollout of Arbitron's Personal People Meter was that the new measuring device would do the same for radio ratings that Nielsen's Local People Meter has done for local TV ratings: knock them down for the bigger stations.

That's exactly what's happening, which becomes clear with the release this week of a new set of results from the PPM in Philadelphia and Houston, the first two markets to switch to the PPM.

The data are startling. Average quarter-hour ratings are off about 30 percent from those under the old paper-diary system, by Arbitron's calculations, and media buyers say the falloff can be as high as 50 percent or more for some stations.

As with Nielsen's LPMs when they began rolling out several years ago, buyers face the prospect of spending more client ad dollars to reach the same audiences they thought they were reaching under the diary system.

Lower ratings translate into lower ratings points, but also more expensive ratings points, since radio stations are not expected to lower prices.

Yet buyers say there's an upside to the new system, which tracks radio listening electronically and passively, making it far more reliable than the diary system, which relied on listeners to remember and write down their radio listening.

They say the overall cost for a radio buy should not change much, if at all.

The reason: With the improved data, buyers can buy deeper down the list of stations and in more dayparts to achieve their reach and frequency goals. The lower costs of those mid-tier stations and lower-demand dayparts, notably weekends, largely offset the higher costs of the top-rated stations and dayparts that made up the bulk of previous buys.

As the PPMs reveal, those mid-tier stations and lesser dayparts are recording higher listening than under the diary system, which tended to favor the big stations and high-demand dayparts. That was because sample listeners were inclined to jot them in when they couldn't remember when they were listening or what station they were listening to.

“We’re using more dayparts, possibly more stations, and certainly the weekend on some stations was a surprising turnaround,” says Janice Finkel-Greene, director of futures and technology at Initiative, the media buying giant. “It makes sense that people were forgetting to enter weekend listening in diaries.”

“We’re doing projections for 2008 and I am projecting buying deeper,” says Rhonda McLeod, senior local buying strategist at Empower MediaMarketing. “At the end of the day, that’s the plan.”

Finkel-Greene says buyers generally feel better prepared for the PPM because of their experience with the rollout of Nielsen's local people meter to replace its old diary system for measuring TV viewing in local markets. That process caused huge disruptions in local markets as buyers struggled to get their arms around the flush of new, more timely TV viewing data, but the result has been much more effective buying, again with deeper buys in many cases.

Arbitron plans to switch the 10 largest markets to PPM by the end of next year. New York is next, in October.

“I don’t think this learning curve will be nearly as long as it was for television,” Finkel-Greene  says. “We got better at it.”

Among its findings from the new data, Arbitron reports that while some highly rated stations are now slipping, there are more top-rated stations than in the past and that many are separated by only a fraction of a rating point. Stations ranging from No. 1 to No. 15 are sometimes separated by only 0.2 rating points.

In Houston in July, for instance, five stations tied for No. 1 on an all-day basis in the 25-54 demographic while four stations trailed at No. 2, separated by only a 0.1 rating point.

Meanwhile, Arbitron also reported this week that its survey sample is falling short of its goals for certain demographic groups, particularly young people.

Arbitron says it’s working to improve its sample and notes that the shortfalls aren’t affecting ratings.

While the move to PPMs is a challenge, media buyers have believed for years the electronic system is more accurate than diaries, which makes the transition, bumpy though it is, easier to accept.

“It’s so much better,” says Finkel-Greene. “How could anybody, with all the media options available now, possibly remember and accurately enter everything they listened to [into a diary]? It’s too hard.”