It turns out that the way information spreads online is often more complicated than viral transmission, in which one person passes a link to, say, a YouTube video directly to another person. As with political topics, people often wait until a number of friends or trusted sources have promoted an idea before promulgating it themselves.

The structure of a social network  for example, whether it is made up of close friends and colleagues or of like-minded strangers who follow Lady Gaga  can have more influence than the size of a group, researchers say.

In real-world terms, that means designers of iPhone apps may be better off trying to get a plug from a leading technology blogger than from Ashton Kutcher, even though Mr. Kutcher has more than six million followers on Twitter. A smaller, more connected network might be more likely to respond to a recommendation from one of its own valued members, says Jure Leskovec, an assistant professor of computer science at Stanford.

In one recent study, for example, Professor Leskovec and a colleague analyzed a set of more than 170 million blog posts and news articles over a one-year period. They identified the thousand most popular phrases in the material and examined how those phrases spread over time via news agencies, newspapers, television and blogs. Content from news agencies tended to spike and gain the most attention immediately, while news that started on blogs or was picked up by bloggers often experienced several peaks or rebounds in popularity as time wore on.

An earlier Stanford study found that bloggers, over time, had more influence than mainstream publications in areas like technology or entertainment.

Professor Leskovec says the studies provide a quantitative way to predict which stories will hold attention and which will fade rapidly, based on who covers the material first. In a few years, he says, “we will be at the stage where marketers will be more mathematical and less intuition-driven.”

The research seems to validate the techniques that many industry experts are already using, says Sunil Gupta, a professor at the Harvard Business School who teaches digital marketing. Marketers are moving from an intrusion strategy of running ads in the middle of TV programs to a more cooperative model in which they try to stimulate discussion across social networks. Automakers that loan next year’s car models to influential car bloggers to test drive are just one example, he says.