The American Community Survey collects data on the college majors of people who’ve graduated college. This excellent data has lots of untapped potential for family research, because it tells us something about people’s character and experience that we don’t have from any other variables in this massive annual dataset. (It even asks about a second major, but I’m not getting into that.)
To illustrate this, I did two data exercises that combine college major with marital events, in this case marriage. Looking at people who just married in the previous year, and college major, I ask: Which majors are most and least likely to marry each other, and which majors are most likely to marry people who aren’t college graduates?
I combined eight years of the ACS (2009-2016), which gave me a sample of 27,806 college graduates who got married in the year before they were surveyed (to someone of the other sex). Then I cross-tabbed the major of wife and major of husband, and produced a table of frequencies. To see how majors marry each other, I calculated a ratio of observed to expected frequencies in each cell on the table.
Example: With weights (rounding here), there were a total of 2,737,000 BA-BA marriages. I got 168,00 business majors marrying each other, out of 614,000 male and 462,000 female business majors marrying altogether. So I figured the expected number of business-business pairs was the proportion of all marrying men that were business majors (.22) times the number of women that were business majors (461,904), for an expected number of 103,677 pairs. Because there were 168,163 business-business pairs, the ratio is 1.6. (When I got the same answer flipping the genders, I figured it was probably right, but if you’ve got a different or better way of doing it, I wouldn’t be surprised!)
It turns out business majors, which are the most numerous of all majors (sigh), have the lowest tendency to marry each other of any major pair. The most homophilous major is theology, where the ratio is a whopping 31. (You have to watch out for the very small cells though; I didn’t calculate confidence intervals.) You can compare them with the rest of the pairs along the diagonal in this heat map (generated with conditional formatting in Excel):
Of course, not all people with college degrees marry others with college degrees. In the old days it was more common for a man with higher education to marry a woman without than the reverse. Now that more women have BAs, I find in this sample that 35% of the women with BAs married men without BAs, compared to just 22% of BA-wielding men who married “down.” But the rates of down-marriage vary a lot depending on what kind of BA people have. So I made the next figure, which shows the proportion of male and female BAs, by major, marrying people without BAs (with markers scaled to the size of each major). At the extreme, almost 60% of the female criminal justice majors who married ended up with a man without a BA (quite a bit higher than the proportion of male crim majors who did the same). On the other hand, engineering had the lowest overall rate of down-marriage. Is that a good thing about engineering? Something people should look at!
We could do a lot with this, right? If you’re interested in this data, and the code I used, I put up data and Stata code zips for each of these analyses (including the spreadsheet): BA matching, BA’s down-marrying. Free to use!
Family Inequality 
It might be interesting to do an analysis by department. Are STEM majors likely to marry other STEM majors? Are Liberal Arts majors more likely to marry each other? I suspect a percieved hierarchy of majors might affect the results.
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Have you ever read any of men’s rights websites? They are obsessed with hypergamy. It would be cool if you or someone disproved this & maybe made a dent in the evolutionary psychology malarkey that they claim hypergamy is evidence for.
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I suspect that people going to less selective schools are more likely to down-marry and that people are more likely to major in criminal justice, education admin, or business at less selective school and if you conditioned on school selectivity most of this effect would go away.
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But surely if you go to a very selective school the odds of “Down marrying” are increased because you are part of a tiny elite…down would have the highest probablility because that’s most everybody else….
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This is no more than vague waffle resulting from an observed correlation. Here’s a hypothesis. Most couples have sex before marriage. Some people do not wish to do so, for reasons of religious belief. I hypothesise that among those who study theology there is a higher than average proportion of religious believers. If an individual wishes to commit, simultaneously, to future marriage and present sexual abstinence, that individual’s best chance of finding someone of identical views is among those of similar religious inclinations, which is more likely if the search is confined to theology students.
If that is the case, it is not the study of theology that leads to marriage to someone with an idential major, but aversion to pre-marital sex. More research needed.
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This is great. Could you perhaps post a higher resolution version of the chart?
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