Online dating sites catalog and categorize vast amounts of user data.
EHarmony uses twenty-nine traits to match its clients with one another, and new members answer over 300 questions as part of the personality test and initial account setup process.
Match.com accounts for 1500 VARIABLES, relying on users' stated and revealed preferences when making recommendations.
OKCupid requires users to answer and rank at least 50 Match Questions before beginning the matching process, and some users report having answered more than 4000.