Then comes the choice to send a person a message, or to reply to one.
Those 30 million people have generated billions of pieces of data.
And because most dating sites ask users to give consent for their data to be used for research purposes, this online courting has played out like an enormous social science experiment, recording people's moment-by-moment interactions and judgments.
Bruch wondered: Is mate selection like a job interview process, where the person with the best combination of positive factors wins?
Or is it more like a -style reality show, where contestants are picked off one by one for a single failing?
But the biggest deal breaker of all turned out to be age, at least for women.
All other factors being equal, women overall were 400 times less likely to browse the profile of a man significantly older than herself. Whereas 20-year-old women were 10 times more likely to ignore a man 10 years her senior, 45-year-old women were nearly 10% more likely to browse the profile of a man 55 or older compared with a man her own age.
"That men care about height at all is, we suspect, a function of their realizing they may get rejected if they aren't quite a bit taller than their potential mates," she adds.
But when it came to body weight, men were less likely to browse the profile of a woman who was heavy-set, whereas women showed little aversion to—with some showing even more interest in—heavier-set men.
Bruch's team devised a statistical model that maps the "decision rules" people follow during the first two steps.
Bruch and her team divided the rules into two broad categories, "deal breakers" and "deal makers," used to exclude or include people for the next level of contact.
View the full list Some time ago, I found myself single again (shock, horror!