Are teen-agers watching more or less TV? A new system for measuring television audiences has found big gains in viewership among 12- to 17-year-olds in major U.S. cities between July 2004 and July 2005, with 30 percent jumps in Chicago and Philadelphia.

Los Angeles, however, was the major exception and officials at the company that tracks television audiences aren’t sure why.

Nielsen Media Research credited the gains in other major cities to the debut of local people meters, which replaced the former diary-based system for reporting viewership with an electronic tracking device.

Nielsen said that because the people meters track viewing information in real time and electronically, they are more accurate than a system that relies on memory and manual record-keeping.

So why did L.A. see a 7.1 percent drop in that age bracket?

“This is just a moment in time July vs. last July,” said Karen Gyimesi, a spokeswoman for Nielsen. “Just because L.A. experienced a decline in the overall day part doesn’t mean there were fewer teen-agers watching television there.”

Still, the Nielsen ratings are the only universal measurement of television viewing and play an important role in programming decisions and advertising rates. Some broadcasters and black and Hispanic activists have complained that the people meters undercount broadcast and non-white audiences, which Nielsen disputes.

In Los Angeles, eight of the top 10 programs among 12- to 17-year-olds are aired on KTTV (Channel 11), which is owned by Fox Broadcasting Co. Fox’s owner, News Corp., has been among the most vocal critics of the people meters. KTTV officials declined to comment.

*

The full Media column

is available in the August 22 edition of the Business Journal.