ending after five years is 20%, for unmarried cohabitators the likelihood percentage is 49%. After 10 years the likelihood percentage for the relationship to end is 33% for married couples and 62% for unmarried cohabitators. One German study found that in regions with high rates of childbirth to cohabitating parents, no negative effect is observed in cohabitation. The study states "union stability of cohabiting mothers is positively related to their prevalence." A 2004 study of 136 couples (272 individuals) from researchers at the University of Denver found differences among couples that cohabited before engagement, after engagement, or not until marriage. The longitudinal study collected survey data before marriage and 10 months into marriage, with findings suggesting those who cohabit before engagement are at greater risk for poor marital outcomes than those who cohabit only after engagement or at marriage. A follow-up survey by the researches of over 1,000 married men and women married in the past 10 years found those who moved in with a lover before engagement or marriage reported significantly lower quality marriages and a greater possibility of a separation than other couples. About 20% of those who cohabited before getting engaged had since suggested splitting – compared with only 12% of those who only moved in together after getting engaged and 10% who did not cohabit prior to marriage. The researchers from Denver suggest that relationships with pre-engagement cohabitation "may wind up sliding into marriage", whereas those that only cohabit post engagement or marriage make a more clear decision. This could explain their 2006 study of 197 heterosexual couples finding that men who cohabited with their spouse before engagement were less dedicated than men who cohabited only after engagement or not at all before marriage. In some heterosexual couples, women are more likely to understand cohabitation as an intermediary step preceding marriage, and men more likely to perceive it without an explicit connection to marriage. An analysis of data from the CDC's National Survey of Family Growth data from 1988, 1995, and 2002 suggests that the positive relationship between premarital cohabitation and marital instability has weakened for more recent birth and marriage cohorts, as the total number of couples cohabiting before marriage has increased. Later CDC work found that between 2002 and 2006-2010, the number of couples in opposite-sex cohabiting relationships increased from 9.0% to 11.2% for women, and from 9.2% to 12.2% for men. Drawing on