Ah, spring! Love is in the air as brides and grooms anticipate the day on which—surrounded by friends and family—they will bow to the economic forces that have brought them together. Love may be the basis of marriage, but it is the market, to a large extent, that brings brides and grooms together and shapes their lives as married couples.

Princeton University alumna Susan Patton caused a stir recently with her open letter urging young female students to lock down an Ivy League man while they have easy access to such high-quality marriage candidates. Whatever you think of this advice in terms of gender politics, one thing is certain: She's got the economics all wrong. It's those Princeton women who hold all the power.

Back when Ms. Patton married in the early 1980s, well-educated women faced a very thin marriage market (that is, a market with few "buyers" and "sellers," as it were). They had to select a husband from a small set of highly sought-after, well-educated men. At that time, men earned significantly more than women. Women's desire to marry up in terms of education made economic sense. In most marriages of the time, husbands earned the high wages, and wives (who earned less regardless of their education) focused their energy on the family.

For women like Ms. Patton, who attended college in the 1970s, the incentive was to find a husband during their years at school, where the marriage market was relatively thick with educated single men—even if that meant compromising on other qualities they might have wanted in a husband. Later in these women's lives, they knew the market would thin and they would have to set their "reservation value"—the minimum set of qualities a man must possess as husband material—at a lower level.

But over the past four decades, economic factors have changed the marriage market in a way that benefits highly educated women.