Although much has been said about the hardworking single mother, the number of single fathers has grown nine-fold during the past half-century — more than twice the rate of growth for single mothers.

Since 1960, the proportion of single parent households led by men has grown to eight percent of all U.S. households in the United States, accounting for nearly one in four households led by a single parent. During the same period, the number of single mothers quadrupled from 1.9 million to 8.6 million in 2011, while the number of single fathers grew from 300,000 to 2.6 million.

Since mid-century, societal changes have led to more divorce and to greater numbers of women bearing children outside of marriage, as well as a greater willingness of courts to grant child custody to the father, as immortalized in the 1979 film Kramer vs. Kramer.

"We have been doing a lot of research here to look at the changing visions of fatherhood," Gretchen Livingston, of the Pew Research Center, told reporters. "We've seen that a father's role is going beyond just the breadwinner. Generally, fathers are being expected to fulfill the same type of things as mothers."

Back in 1960, only 14 percent of single parenthood households were led by fathers, and the vast majority — 92 percent — of households with children had a mother and father raising the children. By 2011, only 67 percent of households with children had both parents in the home.

In a study of U.S. Census Bureau data, the Pew Research Center found measurable differences between the homes of single mothers and fathers, including the greater likelihood of single fathers to cohabitate with a partner. Today, 41 percent of unmarried fathers live with a partner, while only 16 percent of single mothers do the same.

The study also found that single fathers are poorer and less educated than married fathers, with a median income of $40,000 in comparison to $70,000 for their married counterparts. Very few single fathers hold a college degree, at 17 percent, in comparison to 40 percent of married fathers who have a college education. One-quarter of such households live below the poverty line, more than triple the rate for households with married fathers.

However, single fathers are generally more affluent than single mothers, earning $14,000 more than the typical single mother, 43 percent of whom live below the poverty line.

Source: Pew Research Center.

Below is a movie trailer for the 1979 film Kramer Vs. Kramer: