Market share is generally measured in ratings compiled by the Arbitron Company in New York.

By far the most influential measure of audiences are those provided by the Arbitron Company of New York.

Ratings services like the Arbitron Company do not even track the listening habits of youngsters.

The Arbitron Company shut down its experimental national television ratings system yesterday, citing a lack of support from advertisers and network television.

Nielsen's only real competitor in the overnight ratings business is the Arbitron Company, which offers its clients next-day ratings from the nation's 20 largest markets.

According to the Arbitron Company, an audience measurement service, the New York stations with the most listeners are those that focus on music and news.

LEAD: The Arbitron Company said yesterday that its commercial monitoring system will become electronic in the second quarter of next year.

Forty-five million Americans have listened to radio online, according to a recent survey by Edison Media Research and the Arbitron Company.

Until recently she was an account executive with the Arbitron Company in New York.

It is based on research by the Arbitron Company of Manhattan, which tracks how much time people across the nation spend watching television, and which stations they watch.