Arielle Kuperberg digs into some of the patterns behind this trend in "From Countercultural Trend to Strategy for the Financially Insecure: Premarital Cohabitation and Premarital Cohabitors, 1956-2015," written as a briefing paper for the Council on Contemporary Families (October 8, 2018). The briefing paper draws on her article, To cite this article "Premarital Cohabitation and Direct Marriage in the United States: 1956–2015, just published in the Marriage & Family Review (but not freely available online).
Here's the overall trend in cohabitation before first marriage over time.
As Kuperberg breaks down the data, some interesting patterns emerge:
1) Some patterns by education.
"[O]verall there were no significant differences between rates of premarital cohabitation among couples with different levels of education during the period from 1956 to 1986. ... Between 1986 and 2000, premarital cohabitation rates grew more quickly among couples who had not completed high school than among any other group. At the next levels of education, differences in cohabitation rates remained small. Their rates grew more slowly, and there wasn’t a big difference among couples with at least a high school degree over thistime period. ...
"Starting in 1995, a majority of first marriages have begun with premarital cohabitation. Here’s where a new educational divergence occurred: Since 2000, cohabitation rates of the most educated couples have grown markedly more slowly than those of all other educational groups – people with high school diplomas and even ones with some college. By 2011-2015, women who married directly, without first cohabiting, were a minority in every educational group. Even so, marrying directly was twice as common among women with a college degree as among women who had a high school diploma or less. More than 40 percent of women with a bachelor’s degree married in the so-called “traditional” way, without having first cohabited. But fewer than 20 percent of women who had never attended college did so."
2) The link from cohabitation to divorce has shifted.
"[T]he relationship between premarital cohabitation and divorce has also changed over time. Not surprisingly, those who were willing to transgress strong social norms to cohabit from the 1950s to 1970 were also more likely to transgress similar social norms about divorce. Indeed, in that earlier period, people who lived together before marriage were 82 percent more likely to divorce than people who moved in together only after marriage. But as cohabitation became more widespread, its association with divorce faded. In fact, since 2000 premarital cohabitation has actually been associated with a lower rate of divorce, once factors such as religiosity, education, and age at co-residence are accounted for. ...
"Regardless of whether people live together before marriage or not, college-educated couples have far lower rates of divorce than couples with a high school diploma or less. On average, women with a high school diploma or less have a 60 percent chance of a marriage ending in divorce within 20 years. The chance that a woman with a college degree will divorce within the same time period is nearly three times lower — about 22 percent."
3) Economic factors play a role here, too.
As Kuperberg points out, lower rates of cohabitation before marriage for women with higher levels of education in part is likely to reflect higher incomes for themselves or their families. Thus, cohabitation is less likely to arise from economic stress for those with higher education, and marriage prospects are more likely to be taken into account at the start.