But the change will bring a bigger revolution: In a first, Nielsen will simultaneously begin offering three separate sets of TV ratings for each program, reflecting:
* Live, real-time viewing, the same rating system used currently.
* Live viewing plus ratings for programs recorded and played back the same day.
* Live viewing plus playback of recorded programs within seven days of its initial airing.
Nielsen has measured videocassette recording - though not playback - for several years. But until now it has been unable to monitor the more complicated process of viewing in homes with DVRs, which allow users to pause, record and play back shows as they air or much later.
While the number of homes with the devices remains small - only 7 percent to 9 percent of U.S. homes have them - forecasters predict that 10 percent to 25 percent will in five years.
As cable systems and satellite providers aggressively market new boxes with DVR functions, ''it was inappropriate to bypass those homes,'' says Sara Erichson, Nielsen's general manager of national services. ''This is a big change for the industry.''
TV networks - and especially major broadcast networks - have been angling to include them, and claim that Nielsen has left out their most avid, loyal viewers.
Research shows ''people who have DVRs are watching more television and watching proportionately more network television, particularly the top shows,'' says CBS research chief David Poltrack. ''Their exclusion has been hurting the broadcast networks, and we're obviously anxious to get them in the sample.''
Initially, the change will go nearly undetected because only 100 homes with DVRs will become part of Nielsen's sample of 9,000 homes from which national ratings are projected. (Separate samples are used to estimate local ratings). By the start of the new TV season next fall, the national sample will include at least 800 DVR homes, enough to match their proportion of the general population.
In a handful of test cities, the most-often recorded programs in October were ''Desperate Housewives,'' ''Lost,'' ''CSI,'' ''Grey's Anatomy'' and ''Survivor,'' all top-10 shows, while awards shows and sports are mostly watched live. In that early research, including recorded shows boosted overall ratings for top series by an average of 4 percent, CBS says.
But the new ratings data add more wrinkles to the business of selling TV ad time: The networks will seek to charge advertisers for all viewers, but advertisers say they will try to halt increases by arguing that many DVR users fast-forward through commercials. Advertisers are now focusing on ratings for commercials rather than the programs that surround them.
''It's definitely needed,'' says Sam Armando, vice president and director of TV research at media buyer Starcom, of the shift. ''But how it's used, what we agree to use, is still a gray area.''
Nielsen also plans to begin in June measuring viewing of video on demand services.
The move by Nielsen Media Research is a reflection of how the traditional notion of watching TV is changing. If Nielsen's numbers show new technology is also changing what people are watching, it has the potential to profoundly disrupt a multibillion-dollar business.
Channeling
It's a Wonderful Life: KSL Channel 5, tonight, 7. Frank Capra's classic 1946 Christmas tale is told for the last time this year.
I'll Be Home for Christmas: KTVX Channel 4, tonight, 8. Jonathan Taylor-Thomas ("Home Improvement") stars in this 1998 made-for-TV movie about a college student trying to get home for the holidays.
