• by Erik Sass  @eriksass1, October 2, 2009

Seeking to protect its most lucrative markets from poaching by rival measurement firms, Arbitron says it will boost its sample sizes for certain key demos in markets measured by its Portable People Meter over the next couple of years.

Specifically, the media research firm said it will raise the sample size for "persons ages 18-54" by 8% by the end of 2010, and an additional 2% by the middle of the following year, for a total increase of 10%.

In addition, Arbitron says it is committed to achieving and maintaining a sample size of at least 750 active, participating panelists over the age of six in all of the markets measured by PPM by the end of 2011, with the exceptions of Memphis and Providence, where the minimum sample size target will be 675.

The company aims to achieve a milestone of 700 participating panelists for every sample in most markets, and a milestone of 630 in Memphis and Providence, by the end of 2010.

By increasing PPM sample sizes, Arbitron hopes to assuage radio broadcasters that have criticized its sample methodology for PPM ratings. The company has come in for especially pointed criticism from minority broadcasters. They say PPM ratings are based on samples that don't adequately represent minority audiences, leading to big apparent drops in their audiences under PPM measurement. Such drops, they add, threaten their advertising revenues and perhaps their very existence.

After several years of complaints from major radio groups, the controversy grew more heated in 2009 with the involvement of the Federal Communications Commission and Congress.

Rallying political support mostly from Democratic legislators and regulators, minority broadcasters were able to persuade the FCC and Congress to open public hearings into PPM methodology. Last year they also put pressure on Arbitron with the help of attorneys general in New York, New Jersey, and Maryland, who brought lawsuits alleging violation of civil rights statutes. The cases were later settled out of court.

Arbitron is also on the defensive against competition from Nielsen, which is trying to take some of its diary-based ratings business in mid-sized markets, which are too small to justify PPM measurement.

To regain the initiative, Arbitron has announced a number of ambitious new projects over the last couple of weeks. Earlier this week, it unveiled plans for a new cross-platform media measurement group using PPM. And two weeks ago, it announced a new program to create a metric that will gauge consumer "affinity" for both the radio medium in general and for specific radio stations versus their competitors.