The study found that Web sites vary in their average daily visitor reach. One example is retail-oriented messages such as cash-back promotions are more effective when placed on Web sites that have high average daily audience reach and accrue their maximum reach quickly, while branding campaigns do not need that type of speed.

When measured during a span of four weeks, the ESPN and Travelocity Web sites had a reach of 32 percent and 33 percent, respectively, among people who will buy a midsize premium crossover utility vehicle. The ESPN Web site obtains its reach in a shorter amount of time. ESPN brings close to one-third of its total monthly audience in just one day, on average, while the Travelocity site has a daily reach averaging 4 percent.

"Online advertisers who consider average daily audience reach when targeting new-vehicle buyers can quickly determine which Web sites are most efficient for reaching their intended audience and how rapidly their advertising message will be served," said Steve Witten, executive director of marketing/media research at J.D. Power and Associates.

"Optimizing media buys and advertising spot placements in this manner can help advertisers achieve their specific marketing objectives."

The study also found that about 88 percent of new car buyers use the Internet. On average new-vehicle buyers spend 11 hours per week online.

"Since new-vehicle buyers spend substantial amounts of time online, the Internet is a great way to provide branding messages to consumers," said Witten.

"The Internet is especially effective in helping advertisers find ‘in-market’ consumers — those who are actively shopping for a new car or truck — so marketers often overlook the fact that that online advertising is also a particularly effective branding tool."