“There’s only so much you can do with data,” said Susan Etlinger, a research analyst at the Altimeter Group who advises companies on how best to use technology. “There’s always the unknown that has to do with pheromones and human nature.”

But why do you need to sign up for a dating site to meet someone in a bar? Ms. Clapp, a 31-year-old tax accountant, said that the sites acted as a filter, making it more likely that the other attendees were also single, looking for romance and not too creepy. But inevitably, she said, “it’s a little more random than regular online dating.”

The offline events, for members only, are offered as part of their monthly subscription or for a small fee. While many of the events are held in bars, others revolve around activities like learning to make fresh pasta, going on hikes or playing Skee-Ball. Both Match.com, a pay service, and OkCupid, which was bought by Match last year but operates independently, are getting behind the offline idea. Match bought commercial time during the Olympics to promote “The Stir,” as it calls its gatherings. In one ad, which is said to depict scenes from actual Match events, a bubbly blonde asks a new friend, “U.C.L.A.?” and then clinks glasses: “All right, Bruins!”

Match, which has nearly two million paying users, says it has held a few hundred events each month since May in more than 50 cities. OkCupid, which says it has 2.9 million active members, has organized about 100 events in New York since early July and plans to bring the idea to San Francisco, Los Angeles, Chicago and a few other cities in October. It also says it is revamping its business to put events at the forefront.