Researchers at the National Center for Health Statistics estimate that 78% of college-educated women who married for the first time between 2006 and 2010 could expect their marriages to last at least 20 years. But among women who have a high school education or less, the share is only 40%.

The probability of a lasting first marriage is derived from marital history data from the National Survey of Family Growth, a nationally representative sample of women and men who were ages 15 to 44 between 2006 and 2010. Estimates are based on an approach similar to that used to determine life expectancy and assume that marriage patterns in the future will follow patterns today. The findings refer only to opposite-sex marriages; the sample size was too small to analyze same-sex marriages.

Reasons for marriages ending include divorce and separation. Marriages that ended in death were not included in the analysis. One limitation of the survey was that it did not include adults over age 44 and therefore does not take into account long-term marriages that started later in life. And adults with advanced degrees were not separately analyzed because of the small sample size.

The findings are yet further evidence of the marriage gap in the U.S. along educational lines. College-educated adults are more likely to be married than less-educated adults. Among those who were ages 25 and older in 2014, 65% of those with a bachelor’s degree or more were married, compared with 53% of adults with less education, according to a Pew Research Center analysis.