Here's another myth about getting married that just won't die (pun intended). Yesterday, the Washington Post teased its Valentine's Day story with this online headline: "Want to live longer? Try ."

The money quote came from a research brief from RAND: "Numerous studies covering 140 years have shown that married persons tend to live longer than their unmarried counterparts."

As readers of this Living Single blog know, I don't take any quotes at face value. I read the RAND brief and found that it was based on one study of men-only published in 1996. I read that study, too. (The reference to 140 years was alluding to other studies on the topic, including some I'll describe below.)

A book often cited by the Marriage Mafia (Waite and Gallagher's The Case for Marriage) claims that getting married "can literally save your life." In Chapter 2 of Singled Out, I scrutinized each of the studies cited in supposed support of that claim. Here I'll just briefly review some of the tricks the authors used to make the results of getting married look better than they really were.

The most popular cheater method is to pretend that people who are divorced or widowed never did get married. (It is the same method used most often to make the bogus claim that getting married makes you happier or healthier.) Practitioners of this bit of artifice are trying to make an argument that goes something like this: "Divorced people don't live as long as married people, so that shows that getting married expands your life span." But divorced and widowed people DID get married!

Neither the 1996 study based only on men, nor any of the studies cited in The Case for Marriage, compared all of the people who ever got married to the people who stayed single.

So when the authors of The Case claimed that getting married saved men's lives, they did so by acting as if the men who got divorced or widowed did not actually get married. I call that a statistical .

Here's something else interesting from that book. Even after using the cheater method, the authors ended up admitting that getting married did not matter much to women's longevity. Even the women who got married and stayed married did not seem to live longer than the other women.

Now let me tell you the results of what is probably the longest-running study of longevity ever conducted. It is the Terman Life-Cycle Study, started in 1921. The 1,528 men and women, who were 11-years old when the study started, have been followed for as long as they lived. Two groups of people lived the longest: those who got married and stayed married, and those who stayed single. People who divorced, or who divorced and remarried, had shorter lives. What mattered was consistency, not marriage. The results were the same for the men and the women.

Does that mean that once married, you should stay that way in order to live longer? To answer that definitively, we'd have to do a study that could never be done: Randomly assign married people to stay married or get divorced. Maybe those who stayed married would live longer. Or maybe those who wanted to divorce, but were assigned to stay married, would have lives that were even shorter (and more miserable) than those who did divorce. We just don't know.