Oppenheimer died Nov. 2 at her Los Angeles home two weeks after having a stroke and heart attack, said her son, Chris. She was best known for a 1988 study that went against conventional wisdom in explaining why more couples were postponing marriage. With economics playing a greater role for husband and wife, the timing of the 'I do' became more important, according to her research. Her explanation ran counter to the accepted notion that women were marrying later because they had more opportunities in the workplace. 'She argued that uncertainty about the future characteristics of potential mates complicates the process of finding an appropriate spouse and leads to a delay in marriage,' Megan Sweeney, a UCLA sociology professor who specializes in family research, said in a statement. Another study by Oppenheimer concluded in 2003 that a man is more likely to live with a woman than marry her if he is financially unstable. 'I am not saying that people are so materialistic,' Oppenheimer told The Washington Times in 2003. 'What I am really talking about is uncertainty -- uncertainty about what sort of person they are and what the future might be.' She also was the first demographer to document and explain the influx of married women into the workplace after World War II, said Andrew Cherlin, a former student and professor of public policy at Johns Hopkins University. Valerie Constance Kincade was born Oct. 25, 1932, in London and raised in New York City. Her sister, Judith Blake, also studied demographics and was best known for a 1989 book debunking myths that disparage children without siblings. She died in 1993 at age 66. After receiving a bachelor's degree from Vassar College in 1954, Oppenheimer attended the University of California, Berkeley, earning a master's degree in 1962 and a doctorate in sociology in 1966. She taught at UCLA from 1968 until she retired in 1994. For 40 years, she was married to Edward Anthony Oppenheimer, a pulmonologist. He died in 2005. In addition to her son, Oppenheimer is survived by four grandchildren and a great-grandchild. 