Modern American culture is more sexualized than almost any other. Not that there are not cultural enclaves among us of the highly devout, but the MTV watching, I-pod listening, general public are pretty sexualized; and there is little if any stigma to promiscuity, cohabitation or divorce.
Now say that you have ten young women from that MTV modern American secular culture, are the less promiscuous ones less likely to divorce? Who knows? The study has no way of showing such.