Online dating has become the second most common way for couples to meet, but it may encourage a "shopping" mentality in which people become judgmental and picky, focusing exclusively on a narrow set of criteria like attractiveness or interests, says a new study.

The analysis, based on a review of more than 400 psychology studies and public interest surveys, was released online Monday ahead of being published this month in the journal Psychological Science in the Public Interest.

"The internet holds great promise for helping adults form healthy and supportive romantic partnerships, and those relationships are one of the best predictors of emotional and physical health," said Harry Reis, one of the five co-authors of the study and professor of psychology at the University of Rochester.

Online dating has grown rapidly in popularity and social acceptance and is second only to meeting through friends, as a way for singles to connect, but it does have its pitfalls, Reis said.

Comparing dozens and sometimes hundreds of possible dates may encourage a "shopping" mentality in which people focus on a narrow set of criteria like attractiveness or interests, he said. And corresponding by computer for weeks or months before meeting face-to-face has been shown to create unrealistic expectations, he added.

"In the words of one online dater: 'Where else can you go in a matter of 20 minutes [and] look at 200 women who are single and want to go on dates?'"

Among the study's other findings:

• In the early 1990s, less than one per cent of single adult Americans dated online. By 2005, 37 per cent had.
• By 2009, 22 per cent of heterosexual couples and 61 per cent of same-sex couples had found their partners through the web and the figures are likely even larger today.
• Men and women behave differently online. Men viewed three times more profiles than women and men were 40 per cent more likely to initiate contact with a woman after viewing her profile than women were after viewing a man's profile.
• Some online sites tout a "soulmate" search, which "may encourage an unrealistic and destructive approach to relationships," the authors said. People with soulmate beliefs "are likely to exit a romantic relationship when problems arise … and to become vengeful in response to partner aggression when they feel insecure in the relationship," the authors said.
• Online dating sites are not "scientific" as they claim to be. They can't or won't provide the criteria they used to match which profiles a user gets to peruse, the study said. "Instead, research touted by online sites is conducted in-house with study methods and data collection treated as proprietary secrets, and, therefore, not verifiable by outside parties."