Psychology students of the university in Rotterdam have investigated whether people between 15 and 20 years of age tend to be monogamous. This is what they came up with:
Of the girls and guys who have gone steady in the past 25% has slept around during this time.
When people go steady they are less hard on themselves than on their partners. What do they consider acceptable behaviour?

For themselves            For their partner
Going out             91,1%                         62%
Kissing                 39,8%                         9,1%
Necking               17,1%                         1,0%
Intercourse             7,4%                         0,0%