In the 1970s, Jesse Bernard became famous among feminists for arguing that marriage was good for men, but bad for women. The main empirical foundation of her book was a study that purported to show that married women (but not men) were more prone to depression than single women were.
Bernard's study has long been discredited. What the study she cited actually showed was that women who had recently left careers for motherhood were somewhat more prone to depression than were childless working women.
Marquardt and Wilcox now offer current data, which goes further into parental life. They find that single parents are more prone to depression. Married parents, on the other hand, are not. In fact, married women, with or without children, were the least likely to be depressed. Cohabiting parents were also not likely to be depressed. Single women were more likely to be depressed, and most likely of all were single parents - 37% of single mothers, vs. only 22% of married women. This figure controls for age, education, income, and race/ethnicity.
Marquardt and Wilcox's overall conclusion about the affect of parenthood on depression, and on overall happiness, is
the sense of support, solidarity, and meaning afforded by a co-parenting relationship more than makes up for any challenges associated with parenthood when it comes to global happiness and depression.