San Jose, Calif. ? Chemistry? Forget it. Psychology and statistics best determine whether two people will have a happy marriage. At least so claims an online dating service that’s patented its matchmaking formula.

EHarmony.com Inc. this month received U.S. Patent No. 6,735,568, which describes a “method and system for identifying people who are likely to have a successful relationship.”

Not surprisingly, critics and competitors trash eHarmony’s process as overly scientific — some dismissing the so-called “love patent” as gimmicky.

But the patent has also sparked a debate more prickly than whether annual incomes should be included in online dating profiles: Can the elusive art of matchmaking be reduced to equations and databases?

Researchers at Pasadena-based eHarmony, founded by clinical psychologist Dr. Neil Clark Warren, maintain that an individual’s psychological profile is a better barometer of marital success than purely demographic data.

Sites such as TrueBeginnings.com allow users to screen partners through increasingly complex questionnaires, standing apart from the many online dating services that match people according to simple data such as age, religion and education level.

Psychological profiling

EHarmony users answer more than 430 questions, ranging from “Do you smoke?” to “How much does the word ‘dominant’ describe you on a list of one through seven?” and “How often do you feel depressed?”

Researchers compare a person’s score with a “marital satisfaction index” based on the responses of 1,347 couples. Nearly one in five of those couples met on eHarmony, which targets people pursuing a “long-term relationship that leads to marriage.”

EHarmony researchers rank people in 29 categories, including “sexual passion,” “mood management” and “spirituality.” The company will only pair two people when it is 95 percent confident their compatibility rating falls in the index’s top 25 percent. A dominant individual only gets paired with a wallflower if highly compatible in many other areas.

Galen Buckwalter, vice president of research and development, displays an eHarmony.com ad, in his company's offices in Pasadena, Calif. EHarmony.com Inc. on May 11 received what it's touting as the first love

“Opposites might attract, but in our research they don’t stay together,” said Galen Buckwalter, vice president of research at eHarmony, which attracts marriage-minded traditionalists of all faiths and began advertising on Christian radio stations in 2000.

Formula vs. attraction

Other online matchmaking services aim to satisfy a much wider range of motivations for pairings. Not everyone is looking for lasting love. Niche sites abound, spanning a spectrum from die-hard bachelors to Jewish singles, to people who’ve already written prenuptial contracts.

Critics say computerized matchmaking discounts the je ne sais quoi of love in favor of formulas that can seem like basic arithmetic compared to the painstaking psychosexual calculations humans make about mates.

“In the long run, I can certainly see the merit in a questionnaire that helps you make choices about who you date,” said Robin Gorman Newman, a Great Neck, N.Y.-based dating coach and author of “How to Meet a Mensch in New York.” “But it still comes down to attraction as the first step.”

Rivals say eHarmony forces Warren’s research onto people who may have different goals for long-term relationships. Users cannot scroll general lists of members. Many subscribers of eHarmony, which prohibited photos until 2001, still refuse to provide mug shots.

“EHarmony makes claims that their system is the most scientific approach,” said Tim Sullivan, president of Richardson, Texas-based Match.com Inc., the largest online dating service, with 12 million profiles and 1 million subscribers who pay $25 per month. “But we find these claims to be … ridiculous at best.”

Others dismiss the love patent as a marketing ploy. E-commerce companies went on a patent binge starting in the late ’90s, with claims on how to bid for airline tickets (Priceline.com), how to rent DVDs online (Netflix.com), and how to buy a book with a single mouse click (Amazon.com).

EHarmony, which costs $50 per month or $250 per year, doesn’t guarantee a diamond ring — or even a first date. Researchers reject one in five people who complete the free questionnaire and, according to the index, aren’t the marrying type.