But in an upbeat new guide to marriage, For Better, Tara Parker-Pope, a New York Times reporter (and divorcée), devotes a chapter to debunking the 50% stat, at least among the subset of the population that reads books like hers. Since the 1970s, when more women started going to college and delaying marriage, “marital stability appears to be improving each decade,” she writes. For example, about 23% of college graduates who married in the ’70s split within 10 years. For those who wed in the ’90s, the rate dropped to 16%.

According to research at the University of Pennsylvania’s Wharton School, one of the clearest predictors of whether wedding vows will stick is the age of the people saying them. Take the ’80s: a full 81% of college graduates who got hitched in that decade at age 26 or older were still married 20 years later. Only 65% of college grads who said I do before their 26th birthday made it that far.

But just 49% of those who married young and did so without a degree lasted 20 years, a cohort that Parker-Pope spends little time discussing. Instead she contends that the 50% stat is a myth that persists because it’s something of a political Swiss Army knife, handy for any number of agendas. Social conservatives use it to call for more marriage-friendly policies, while liberals find it handy to press for funding for programs that help single moms.