Nielsen announced the data as part of its preparations to release commercial viewing numbers for every TV program, starting in May. Nielsen, which collects data every few seconds through its set-top boxes, added DVR households to its sample in the last year; its commercial ratings data reflects the total time viewers spend watching ads, including viewing of partial ads, rather than whether ads are watched from start to finish. Advertisers spent upward of $70 billion last year for their TV spots — more than in any other type of media.

“The cable operators that have the subscribers, the programmers who have the content and the marketers have to get ahead of this,” said Curt Hecht, chief digital officer at GM Planworks, the part of the Starcom MediaVest Group that manages General Motors’ ad buying. “They need to figure out how advertising can remain sustainable and effective in the new landscape.”

Advertising and television executives have not yet figured out which DVR owners are more likely to be commercial skippers, though Nielsen has found that younger people generally skip more commercials and time-shift more of their viewing than older people.

Nielsen has also found that commercials are more often watched during playback if the viewer is looking at the show the same day it ran. Commercial viewing drops significantly over time after the original showing. If advertisers start paying for DVR viewing, one question is whether they will pay just when viewers play back shows within a few hours.

Without DVRs, people can, of course, change the channel, leave the room or not pay attention during commercial breaks, but those activities seem to have only a minor effect on ratings during commercials — only 5 percent, according to Nielsen data.

“DVRs are really the big X factor going forward,” said Brad Adgate, senior vice president for research at Horizon Media, an ad-buying agency. “People’s DVR behavior is going to drive the marketplace.”

DVRs, which were introduced in 1999, are becoming more popular every year, and the cable operators are increasingly offering the feature in new set-top box packages. Analysts say DVRs are now in 12 to 20 percent of households. DVR owners tend to be wealthier and more educated than the average TV owner. DVR owners tend to have more children, and some own more than one DVR.