For the first time, a significant portion of the U.S. online audience for prime-time TV content is not watching part of the show on television, according to a new study from Integrated Media Measurement Inc.

Up to 20 percent of U.S. TV viewing happens online, and some viewing levels are higher than levels via DVR playback. According to IMMI, half of these viewers consider online viewing as a “TV replacement,” 31 percent say online viewing is to “catch up” on missed programmes and some 18 percent categorise it as “fill-in viewing”, MediaPost reported.

The study also shows online TV viewers are less likely to use a DVR compared to traditional live TV viewers. About 30 percent of traditional live TV viewers use a DVR on a regular basis, while only 22 percent of online TV viewers do so, according to the study, MediaPost reported.

IMMI pointed out that higher viewing levels online are for some content, not necessarily complete episodes, for example, sampling of shows.

Although online viewing of programmes are higher than DVR playback, DVRs are only available in about one-third of the country, while online access penetrates about 82 percent of U.S. households.

In accord with other research, the online viewer tends to be younger than the average traditional live TV viewer. According to IMMI, those between ares 45 to 55 account for one-fourth of live viewing - the biggest age group of all. For online viewing, 25- to 34-year-olds make up 30 percent, the most of any demographic, Media Post reported.