Ever since US Internet usage became widespread, marketers have been tracking online usage to see if Web time was coming at the expense of TV time.

Now, IDC has found that Internet is the medium on which US online users spend the most time–32.7 hours per week, almost twice as much as they spend watching television. The data was collected in September and October 2007.

Now, People Spend Twice as Much Time Online as Watching TV

“The time spent using the Internet will continue to increase at the expense of television and, to a lesser extent, print media,” said Karsten Weide, program director at IDC. “This suggests that advertising budgets will continue to be shifted out of television, newspapers, and magazines into Internet advertising.”

Average Time per Week that US Internet Users Spend with Select Media, September-October 2007 (hours)

This sounds like the trumpet of doom being sounded for TV viewing and the ad dollars that go with it.

But that’s not the whole picture.

The press release accompanying IDC’s findings said that the company used a sample of “US residents 15 years of age or older who frequently use the Internet.” Since the release did not state what this group’s TV viewing habits were in the past, the only conclusion that can be drawn is that this group of heavy Web users is online for more time than they watch TV.

The study makes no mention of multitasking.

IDC’s findings of time spent online do agree with other studies. comScore Media Metrix found that Internet users spent an average of 29.34 hours online from October 2006 to October 2007. The company surveyed a more general online population than IDC did, not just frequent Internet users.

During September and October 2007, when the IDC study was conducted, US Internet users surveyed by comScore Media Metrix tallied an average of 29.51 hours online.

Time Spent Online by US Internet Users, October 2006-October 2007 (millions of total minutes per month and average minutes per user)

The USC Annenberg School Center for the Digital Future put time spent online by US Internet users at an average of 15.3 hours weekly in 2007. USC’s findings were specific to home usage, and did not include work or school usage.

USC said that it did not subtract time spent at home doing work, since it said that time spent for personal online usage at work balanced it out.

How do IDC’s heavy Internet user media usage numbers compare with media usage by the general population?

Forrester Research examined time spent by US adults on various media in 2007. The research company found that, including personal and work usage, time spent online still trailed time spent watching TV.

Although TV ad spending as a percentage of all media ad spending trailed TV viewing time as a percentage of time spent with all media slightly, the corresponding difference between time spent online and Internet ad spending was still profound, at nearly 4 to 1.

Share of Time in a Typical Week that US Adults Spend with Select Media* vs. Share of US Advertising Spending by Media, 2007

Comparing the IDC and Forrester data suggests that each set of findings should be read for what they are. In IDC’s case, the notion that heavy Internet users spend much more time online than on TV is a cue to marketers targeting such users.

The Forrester numbers provide a reality check, however, suggesting that TV ad spending is not set for an immediate exodus to the Web. Online ad spending still greatly trails online usage as a percentage of time spent compared with other media, but TV is still the media of choice for US consumers as a whole.

Via eMarketer