According to a recent study by RAND sociologists Michael Pollard and Kathleen Mullan Harris, living together before marriage often fails, WORLD reports. The study surveyed 1,500 couples -- divided equally between those who were dating, living together, and married -- for a history of marriage and "marriage-like" relationships (defined as living together for over a month). The study's authors tracked a sample of respondents from 80 high schools and 52 middle schools, beginning in 1995 and following up periodically. The researchers found that by age 23, half of females had cohabited with someone. Males followed a similar pattern, with half having cohabited by age 25. The study then measured feelings of commitment and intimacy for cohabiting couples. It found couples in cohabiting relationships, even long-term ones, never achieve the closeness of married couples. For example, even after living with a partner for over a year, about 20 percent of males keep another, separate residence. Also, only 40 percent of women who cohabit have made a purchase of more than $500 with their partners, while 80 percent of women in marriages have made similar purchases. In every measure of consolidation, intimacy and commitment, couples who are living together feel less closeness than married couples. Fewer share resources and 18 percent are not dating their partners exclusively. More than twice as many are not sure if their relationship is permanent. The low commitment levels in cohabiting are particularly tough on females. Women agreeing to move in with a partner typically look for a deeper, more committed relationship, but according to the study, their hopes are often unfulfilled. While both genders reported less commitment than married couples, cohabiting males show significantly less commitment on all four measures, and 52 percent are not "almost certain" their relationship will last. Along with lower commitment, significantly fewer cohabiting males say they agree with the statement "loves partner a lot."