The marriage rate in the United States is continuing its decades-long downward slide, with fewer American women than ever getting married and others waiting longer to wed, LiveScience reports. The marriage rate has fluctuated in the past, with dips in the 1930s and 1960s, but it has been in steady decline since the 1970s. Now, researchers report that the marriage rate has dropped to a new low of 31.1, meaning there are about 31 marriages in the U.S. for every 1,000 unmarried women, researchers found. In 1950, that number was 90.2. In 1920, it was 92.3. "Marriage is no longer compulsory," said study researcher Susan Brown, co-director of the National Center for Family and Marriage Research at Bowling Green State University. "It's just one of an array of options. Increasingly, many couples choose to cohabit and still others prefer to remain single." To calculate the marriage rate, researchers look at the percentage of women older than age 15 who get married each year, so the plummeting numbers could also be explained, in part, by Americans delaying marriage longer than they have in the past. A woman's average age at first marriage in the United States is now nearly 27, the highest in more than a century, according to the report. Still, among all American women over 15, less than half (47 percent) are married today, the lowest since the turn of the 20th century, and down from a peak of 65 percent in 1950, the report found. On the other hand, the proportion of women who are separated or divorced is on the rise, at 15 percent today, compared with less than 1 percent in 1920, the researchers say. "The divorce rate remains high in the U.S., and individuals today are less likely to remarry than they were in the past," Brown said.