NEW YORK - The radio ratings company is pressing ahead with the 50-city roll-out of its portable People Meter, despite the withdrawal of key test partner Nielsen Media Research.
   Arbitron claims the device will provide the most accurate measurement yet of which radio stations people listen to and for how long.
   Says president/ceo Steve Morris: "There's an urgent need to respond to advertisers who are looking for accountability and precision. We need to have something we can move forward with today."