• by Erik Sass  @eriksass1, December 21, 2009

The battle for the hearts, minds and wallets of radio broadcasters continues. Arbitron, the incumbent radio ratings research firm, is moving the date forward for its planned increase in target sample sizes for cell-phone-only households in its diary markets. Previously scheduled to take place near the end of 2010, the date for the increase in cell-phone-only samples has been moved to sometime this spring.

The move will raise the average target sample size for cell-phone-only households from 10% to 15% of panelists in all Arbitron's diary markets where ratings are based on self-recorded paper diaries of radio listening maintained by panelists.

It should be noted that the 15% figure represents a national average across all Arbitron markets, implying that individual markets may have a higher or lower proportion of cell phone-only households.

Separately, Arbitron has also revealed plans to raise the proportion of cell phone-only households in its Portable People Meter markets to 20% by the end of 2010. (PPM, an electronic measurement device, is only being deployed in the 50 largest markets because of its high cost, which makes it prohibitively expensive for mid-sized markets.)

With these increases, Arbitron aims to provide a more accurate picture of radio listening by young adults, who have been ditching home landlines in favor of personal cell phones in increasing numbers. It also comes as Arbitron faces new competition from Nielsen, which jumped into the radio ratings arena earlier this year.

Nielsen is touting its sticker-based diary system for radio ratings in mid-sized markets, claiming the stickers are more accurate than handwritten diary entries. Nielsen has also boasted of the high proportion of cell phone-only households in its audience panels -- an average 15%.

Over the last year, both media ratings firms have been wooing radio broadcasters with research findings that support radio's ad sales position, demonstrating its wide reach and frequent listening among American adults -- especially 18-34s, who are most likely to be in cell phone-only households.