Prettier Than Napoleon

Interesting results of a study comparing STD rates among teens who make virginity pledges and those who do not. What is the utility of a public pledge against essentially private behavior? Peer pressure not to violate the pledge seems minimal, due to a lack of information about who is breaking their pledge. The only sure-fire way to know peers broke their word is for girls to get pregnant, and then it's literally all over but the shouting. In any case, high pledge rates probably correlate highly with communities that have abstinence-only sex ed. I'd like to see if the results hold for those with more substantive sex ed programs.