I mean, I'd start at the very question - romantic desire? I mean, were they testing against likelihood for partners to make out? Go home and sleep together? Go on second dates? Admit mild attraction but not instigate further action? Date a whole lot and eventually break up? Or marry?

The things people look for in a partner to go home with for the night are different from the things people find "just generally attractive" (oh he's hot) which are different from the things people find good for long-term dating. I mean, obviously, but my point is the layer of complexity doesn't just start at "different things that cause attraction."