The headline of a recent Yahoo Parenting article, “Why Friends Make Moms Happier Than Husbands,” immediately captured my attention as a married mother of two. It highlights the findings of a new study from two Arizona State University (ASU) researchers, who used an online survey of over 2,000 mostly well-educated mothers to determine the key factors associated with their psychological health. The Yahoo article zeroed in on the study’s finding that “being married, per se, was not related to the mothers’ psychological well-being,” and emphasized that support from friends had a stronger influence on the surveyed moms’ happiness than spouses.

In an ASU article touting the study, lead author Suniya Luthar, a psychology professor, also appeared to downplay the influence of marriage to mothers’ mental health, stating that, “Relationships with spouses are important but clearly not determinative to a mother’s well being. Our findings show the strong potential protective power of other close relationships.”

The finding that mothers benefit greatly from supportive relationships makes perfect sense to me as a parent. I always feel better about how I am doing in my job as a mom when I share problems with other mothers in my circle of friends—women who offer a level of emotional support that frankly my husband does not.

But the study’s claim about the impact of marriage is surprising because it appears to contradict a large body of research showing that marriage itself positively benefits the mental health of parents. On a personal level, it also bothers me because I was raised by a single mom, who faced higher levels of fatigue and stress from parenting solo than I will ever experience as a married mom. Although she had a lot of emotional support from female family members to help sustain her, these relationships were not a replacement for the support that only a husband and father can provide.

A closer look at the ASU study, which was published by Developmental Psychology last month, is helpful in understanding what it found—and its limitations. The study, “Who Mothers Mommy?: Factors That Contribute to Mothers’ Well-Being,” is not based on a nationally representative or random sample of mothers, but on an online survey of women who were recruited through PTA groups, college campuses, and other means with the intention of finding “relatively well educated women.” Most moms who participated had family incomes of $75,000 or higher (well above the U.S. median household income of roughly $52,000), and 84 percent had at least a college degree (versus 30 percent of the general adult population). Additionally, 85 percent of the surveyed mothers were legally married.

The goal of Luthar and her coauthor, Lucia Ciciolla, was to determine whether mothers benefit more from personal support or their feelings about themselves as parents, and to discover what factors contribute to their mental health. They discovered that having strong personal support from others, especially friends, had as much and sometimes more of an impact on mothers’ mental well-being than how they felt in their role as mothers. They also identified four predictors most associated with mental health for mothers—“friendship satisfaction, authenticity in relationships, feels seen/loved, and feels comforted”—and found that “satisfaction with the frequency of visiting with friends had significant unique associations with all seven adjustment outcomes” (i.e., anxiety, depression, stress, emptiness, loneliness, life satisfaction, and fulfillment).

Luthar and Ciciolla reported that there was “scant evidence for the benefits of being married per se,” except for “a unique association with [higher] life satisfaction,” particularly for mothers who were married and satisfied with their partners. Importantly, since the overwhelming majority of moms in the study were married, it also found a strong association between partner satisfaction (married/unmarried) and life satisfaction, and showed that partner satisfaction helped to reduce stress and emptiness. For example, when the moms were asked, “When you are very distressed, who tends to bring you the most comfort?”, 50 percent chose “spouse/partner,” while 28 percent chose “relative or friend.”

Regarding marriage, the study claimed that “being married in itself is not necessarily protective [for mothers’ mental health]; what benefits women more is that they feel loved and comforted when in need—whoever the source of those feelings.” This statement is misleading, to say the least. That’s because in examining the link between marriage and mental health, Luthar and Ciciolla control for these feelings, as well as family income and the quality of mother-child relationships. It turns out that their own data indicate that married women are more likely to report feelings of love and comfort than unmarried mothers, and they also report higher household incomes and better relationships with their children. It’s true that researchers often disagree about what variables to include as controls. But as Matthew Yglesias once explained at Vox about the gender pay gap, sometimes statistical controls that seem to make a link disappear (whether the link between marriage and positive outcomes, or the link between gender and income) actually reveal what underlies the link. It is striking that the very factors Luthar and Ciciolla highlight as key predictors of maternal well-being are actually higher among married mothers in their study.

Marriage Matters to Mental Health

Despite the limited association between marriage and happiness in this recent study of well-educated women, a myriad of nationally representative, longitudinal studies have established that marriage itself is a key factor in mental well-being for both women and men.

Sociologist Robin W. Simon, Ph.D., a Wake Forest University professor who has studied marriage and mental health for over 25 years, noted in a 2012 interview with Psychiatry Weekly that “hundreds of studies document a robust relationship between marriage and improved mental health: married people report significantly fewer symptoms of depression and are significantly less likely to abuse substances than their non-married counterparts.” According to Simon, married people enjoy greater social support and psychosocial (or coping) resources than unmarried people.

In a 2007 research brief for the Institute for American Values, W. Bradford Wilcox, Linda J. Waite, and Alex Roberts summarize the vast body of research on marriage and mental health to show that on average, married men and women exhibit better emotional and psychological well-being, and lower rates of substance abuse, depression, and suicide, than single or divorced individuals. They cite a 10-year study of 14,000 Americans that found that “marriage is one of the most important predictors of happiness.” Importantly, the protective power of marriage on mental health holds true in several longitudinal studies, even after controlling for prior mental health and other demographic characteristics. More recently, a National Bureau of Economic Research working paper issued in 2014 found that “even when controlling for pre-marital life satisfaction levels, those who marry are more satisfied than those who remain single.”

Looking specifically at parents, a 2011 report from the National Marriage Project, When Baby Makes Three, used national surveys to demonstrate that married parents ages 18 to 46 are more likely than single parents to say they are “very happy” with life, and single parents in their mid-twenties are 13 percentage points more likely to report depression than married and cohabiting parents in the same age range.

As to why marriage matters to mental well-being, Wilcox, Waite, and Roberts explain that marriage provides “a source of social support, [such as] someone to talk to about the troubles of life,” and “increases married people’s sense of meaning and purpose in life, protecting against suicide, depression and anxiety, and encouraging healthy habits.” They also point out that the expectation of commitment and permanence in marriage provides a unique sense of support that other relationships do not provide. And of course, parenting with a committed partner, especially within a marriage, is simply easier than parenting alone.

The ASU study’s highly selective sample and choice of control variables help explain its finding that being married had less impact on these mothers’ mental well-being than friendship support. While the study is useful in underlining the importance of supportive relationships to mothers’ happiness, in no way do its findings diminish the well-established independent association between marriage and mental health found in hundreds of other studies.

In fact, the ASU’s study’s central conclusion that moms benefit most from knowing they are loved and feeling comforted is more evidence for why marriage matters to overall well-being, and especially to parental happiness. That is because the support and comfort that moms need to thrive is best cultivated in a marriage where the tasks of parenting are not borne alone but shared with a child’s father. As the National Marriage Project report put it, “the meaning, social support, financial security, and stability afforded by marriage … make life more enjoyable for today’s parents.”