Cohabitation in the United States is loosely defined as two or more people, in an intimate relationship, who live together and share a common domestic life but are neither joined by marriage nor a civil union.
Statistics
In most parts of the United States, there is no legal registration or definition of cohabitation, so demographers have developed various methods of identifying cohabitation and measuring its prevalence. The Census Bureau currently describes an "unmarried partner" as a "person age 15 years and over, who is not related to the householder, who shares living quarters, and who has a close personal relationship with the householder." Before 1995, the Bureau identified any "unrelated" opposite-sex couple living with no other adults as "POSSLQs", or Persons of Opposite Sex Sharing Living Quarters, and the Bureau still reports these numbers to show historical trends. However, such measures should be taken loosely, as researchers report that cohabitation often does not have clear start and end dates, as people move in and out of each other's homes and sometimes do not agree on the definition of their living arrangement at a particular moment.
In 2001, in the United States 8.2% of couples were calculated to be cohabiting, the majority of them in the West Coast and New England/Northeastern United States areas.
In 2005, the Census Bureau reported 4.85 million cohabiting couples, up more than ten times from 1960, when there were 439,000 such couples. The 2002 National Survey of Family Growth found that more than half of all women aged 15 to 44 have lived with an unmarried partner, and that 65% of American couples who did cohabit got married within 5 years.
In 2011, the Census Bureau reported 7.6 million opposite-sex cohabiting couples in the country with a separate report listing the number of cohabiting same-sex couples at 514,735 as of the 2010 Census.
The cohabiting population includes all age groups, but the average cohabiting age group is between 25 and 34.
Stability
In 2003, a study was made of premarital cohabitation of women who are in a monogamous relationship. The study showed "women who are committed to one relationship, who have both premarital sex and cohabit only with the man they eventually marry, have no higher incidence of divorce than women who abstain from premarital sex and cohabitation. For women in this category, premarital sex and cohabitation with their eventual husband are just two more steps in developing a committed, long-term relationship." Teachman's findings report instead that "It is only women who have more than one intimate premarital relationship who have an elevated risk of marital disruption. This effect is strongest for women who have multiple premarital coresidental unions."
A survey, conducted by researchers at the University of Denver (2009), of over 1,000 married men and women in the United States found those who moved in with a lover before engagement or marriage reported significantly lower quality marriages and a greater possibility for splitting up than other couples. About 20 percent of those who cohabited before getting engaged had since suggested divorce – compared with only 12 percent of those who only moved in together after getting engaged and 10 percent who did not cohabit prior to marriage.
Psychologist Dr. Galena Rhoades said: "There might be a subset of people who live together before they got engaged who might have decided to get married really based on other things in their relationship – because they were already living together and less because they really wanted and had decided they wanted a future together. We think some couples who move in together without a clear commitment to marriage may wind up sliding into marriage partly because they are already cohabiting."
A 2001 study of 1,000 adults indicated that people who cohabited experienced a divorce rate 50% higher after marriage than those who did not, though this may be correlation and not cause-and-effect. A subsequent study performed by the National Center for Health Statistics with a sample size of over 12,000 individuals found that there was no significant difference in divorce rate between cohabitating and non-cohabitating individuals.