Excerpt from this article:
“Where eHarmony varies dramatically is communication,” Piskorski told me in a recent telephone interview. “People reach out to each other more on eHarmony, and get more responses on there. The people you traditionally would think have the hardest time reaching out to people do very well on eHarmony.”
In his book, Piskorski explains that older women and a subgroup he categorizes as “men who are shorter, older, or overweight” are more likely to send messages to potential partners on eHarmony than on OKCupid. He attributes that to the different demographics which use eHarmony, but he says most of it is due to the site’s design. Because users are connected with a relatively small pool of partners–rather than letting them pursue the entire site as in OKCupid’s case–he feels that encourages otherwise timid users to go ahead and message.