NEW : Study 's top researcher cautions there is no concept of cause and effect . More than three hours a day qualifies as email . -- nearly 3.5 times more likely to have had sex . More than three hours a day on Facebook would be considered email .
NEW : Study 's top researcher cautions there is no concept of cause and effect . More than three hours a day qualifies as email . More than three hours a day on Facebook would be considered email .