Since 1967, the median household income in the United States has risen modestly, fluctuating several times. Even though personal income has risen substantially and 42% of all household now have two income earners, the median household income has increased only slightly. According to the US Census Bureau, this paradoxical set of trends is due to the changing structure of American households. For example, while the proportion of wives working year-round in married couple households with children has increased from 17% in 1967 to 39% in 1996, the proportion of such households among the general population has decreased. Thus, while married couple households with children are the most economically prosperous type of household in the United States, their share of the population has been dwindling in the United States. In 1969, more than 40% of all households consisted of a married couple with children. By 1996 only a rough quarter of US households consisted of married couples with children. As a result of these changing household demographics, median household income rose only slighly despite an ever increasing female labor force and a considerable increase in the percentage of college graduates.