Ladies: It’s not you. It’s the ratio.

When journalist Jon Birger worked in the newsrooms at Fortune and Money, he noticed that most of the guys either had wives or long-term girlfriends, whereas most of the women were single and “had dating histories that made so little sense to me,” as he put it in a recent interview in Los Angeles.

His new book, “Date-onomics: How Dating Became a Lopsided Numbers Game,” attempts to address the question of why it seems so hard for women in their 20s and 30s to find a life partner. The answer? There are significantly fewer men on the market. 

Specifically, Birger found, significantly fewer college-educated men than college-educated women. He cites U.S. Census data and other publicly available sources indicating that among college graduates between 22 and 29, there are about four women for every three men. And between 30 and 39, there are five college-educated women for every four college-educated men. 

As Birger points out, this wouldn’t be a problem “if we were all more open-minded about who we were willing to date and marry.” But in a world where college-educated men and women are more likely to live in the same neighborhood and congregate at the same bars, the imbalance Birger explains in “Date-onomics” has significant implications. Particularly in big cities where the imbalance strongly favors men (such as Manhattan and Los Angeles, where there are 39 percent and 24 percent more women than men with college degrees, respectively), guys tend to play their market advantage by keeping their options open, he argues.

In an interview with the Journal while in town from New York to promote his book, Birger suggested some solutions to the gender imbalance, offered some practical advice for women and discussed how demographics have even influenced the dating markets of Orthodox Jews:

Jewish Journal: For a female college grad in her 20s who wants to find a husband in today’s dating market, what’s one suggestion you have based on your research?

Jon Birger: If marriage is a big priority for you, I guess I might suggest getting serious about dating younger instead of putting it off until you’re in your mid- 30s. And the reason I say that is, every year the dating math is going to get more challenging. In the book, I liken it to musical chairs. In the first round of musical chairs, only the kid who’s not paying attention doesn’t get a chair, but by the last round of musical chairs, you have a 50 percent chance of losing, and something similar happens in dating. If you start out with a dating pool of 14 women and 10 men, once six women and six men pair off together, the ratio among the remaining singles becomes 2-to-1. Every time two people pair off and pull themselves out of that lopsided singles market, the math gets more challenging for the women and better for the men. 

JJ: Is there a point where physically relocating can improve a woman’s odds? 

JB: Clearly, a woman who doesn’t put a maximum priority on marriage is probably not going to pick up her whole life and give up her job and her friends and family just to move someplace where the odds might be better. But if it’s a situation where maybe she was thinking about moving anyway and, as your question kind of assumes, marriage is kind of a really high priority for her, yes, I can see moving to Denver, Seattle, Silicon Valley — because the dating math is more appealing there. One smaller move they can make, it’s not even a move … in general, suburbs tend to have less imbalanced sex ratios among college grad singles than urban centers do. So if you’re online dating, even just expanding your geographic search to include outlying areas, that’s an easy way to take advantage of more favorable sex ratios. 

JJ: Are there any macro solutions to this imbalance?

JB: No. 1 is a long-term solution. It’s getting more young men, more boys to go to college. That won’t solve the dating problem for people who are single in their 20s and 30s now, but it’s not a good thing either for the dating world or for the economy, frankly, that boys aren’t going to college in the same numbers as girls. There’s a lot of research, neuroscience, showing that boys’ brains mature at a slower rate than girls’. Both intellectually and socially, they lag about a year behind girls, and there are some countries where both boys and girls start first grade later than they do here in the U.S. Interestingly, in those countries, the college gender gap is more narrow, and that tells me that if you give the boys a little more time to catch up, they will. So, one idea here would be to basically “red shirt” boys. This is something that would have to come from the parents because under Title IX, public schools could not say boys are starting at 7 and girls are starting at 6. 

JJ: Can you explain the so-called “shidduch crisis” in the Orthodox community?

JB: Each one-year age cohort in the Orthodox community has about 4 percent more people than the one that preceded it. That only matters because within one part of the Orthodox community, what I call the “yeshivish” community, some people call it Lithuanian … there’s a traditional age gap at marriage, so you’ll have 21- or 22-year-old men marrying 18- or 19-year-old women. … As a result, there’s about 10 to 15 percent more women who are entering the matchmaking process than there are men who are entering the matchmaking process. And the “shidduch crisis” basically refers to these excess women who are unable to find marriage matches, and within the community it’s become a source of great angst, particularly for the young women and their parents. 

JJ: But this “crisis” doesn’t exist in the Chasidic Jewish community, right?

JB: Their tradition is, while everybody marries young, they marry people their own age. Eighteen-year-olds marry other 18-year-olds, so even though they have a very high birthrate, too, you don’t have this demographic mismatch of lots of 18-year -olds trying to find matches with too few 21- or 22- or 23-year-olds.

JJ: You suggest in the book that the “marriage ultimatum” can be a useful tool for women, particularly in this imbalanced market. Can you explain that?

Birger: It’s kind of mean for a guy to be dating a woman in her late 30s for two full years without actually marrying her. I interview a really smart young matchmaker in the book … she has a line, she calls guys like these “time thieves,” and she’s right. For a woman in her late 30s or early 40s who really wants to have kids, and she hears her biological clock ticking, letting these relationships drag on without getting a ring, it feels counterproductive. 

From the guy’s perspective, in business and politics, you hear all the time, “You should never make a decision sooner than you have to.” And that’s actually good life advice, but when you apply it to dating from the perspective of a man, a man might conclude, “Well, I’m going to keep my girlfriend as an option while continuing to survey the market, because I don’t have to make a decision.” What an ultimatum does is force him to make a decision and it creates artificial scarcity in an otherwise abundant marketplace. Essentially, it makes you want more of what you fear you may lose. So, I think ultimatums work in business, they work in all kinds of life contexts. It does seem as if the women who are firm are more likely to be successful in getting the guy to settle down.