While the basic unit of the family has proved remarkably resilient, there have been considerable changes in typical family structure across the last few decades, at least in the developed Western world. For one thing the percentage of single households has increased dramatically. As people are marrying later and divorcing more frequently, people are living alone for longer periods of their life. Nonetheless, married couples with or without children still comprise the most common family structure. According to the 2000 census, married couples account for more than half of U.S. households, while single people accounted for more than one quarter. Unmarried partners of both the same and opposite sex, three generational families, and single parents with children also make up a large segment of American households. Furthermore, blended families—such as combinations of previously divorced families—are also very common.