Maternal employment and overweight children
Introduction
Being overweight may be one of the most significant health issues facing American children today.1 Over the past three decades, weight problems among children have grown so dramatically that observers routinely describe the trend as an epidemic. In the 1963–1970 period, 4% of children between the ages of 6 and 11 were defined to be overweight; that level had more than tripled by 1999, reaching 13% (Centers for Disease Control, 2001).
This general trend masks important differences in the prevalence of childhood weight problems by socioeconomic status. For example, only 1.7% of black boys were recorded as being overweight in the 1963–1965 period, but that rate has grown almost 10 times to reach 15.1% in 1988–1994 (National Center for Health Statistics, 1998). By 1988–1994, 18.8% of Mexican American boys, 17.4% of black girls, and 11.7% of white girls were overweight. As we show subsequently, the fraction of children who are overweight is much higher for the poor and for those with less educated parents as well.
Researchers and public health officials are currently at a loss to explain the rapid rise in weight problems among children. At some basic physiological level, the cause of this increase in overweight status among children is clear: weight gain is attributable to taking in more energy than one expends. What is unclear is what has upset this balance between energy intake and expenditure over the last three decades.
It is important to consider what causes a child to be overweight, including the environmental factors that may affect either the intake or expenditure of energy. In this regard, analysts have tended to point to factors like the availability and consumption of calorie-rich fast foods along with increased television viewing and decreased exercise. These explanations beg the question of why these behaviors have changed, however, since fast food and television have both been available for decades.
Popular opinion routinely draws a direct link between mothers working and poor health and social outcomes for children. Typical comments express concern about the effects of child care, for instance warning that “parents who casually warehouse their kids could use a healthy DOSE of anxiety (Feder, 1999).” According to the Washington Post, “two-thirds of the people surveyed said that although it may be necessary for a mother to work, it would be better for her family if she could stay home and care for the house and children (Grimsley and Melton, 1998).” Popular news reports on the topic of overweight children are similarly peppered with comments from health practitioners who either implicitly or explicitly attribute changes in children’s diet and exercise to the increased likelihood that both parents work outside the home. For example, a 1999 Boston Herald article cited a pediatric nutrition specialist who “noted in particular that dual-career couples are spending less time monitoring their latchkey children, who consequently snack after-school, using their often liberal allowances on candy, ice cream, or soda pop (Mashberg, 1999).” Popular nutrition author Dr. Andrew Weil in an interview on CNN attributed the increased reliance on prepared and processed foods to the fact that “typically, people say they don’t have time to cook.” The interviewer attributed this time constraint to the prevalence of dual-career families (Weil, 2002).
Those who believe that dual-career families may be contributing to changes in children’s diet and exercise habits have a compelling prima facie case. The rise in women working outside the home coincides with the rise in childhood weight problems. From 1970 to 1999, the fraction of married women with children under six who participate in the labor force doubled, rising from 30 to 62%. Married women with children ages 6–17 dramatically increased their labor force participation as well, rising for this group from 49 to 77% over this period (US Bureau of the Census, 2000).
There are several potential mechanisms through which children’s eating patterns and level of physical activity may be affected by having parents who work outside the home. Child care providers may be more likely to offer children food that is highly caloric and of poor nutritional value. Further, parents who work outside the home may serve more high-calorie prepared or fast foods, and unsupervised children may make poor nutritional choices when preparing their own after-school snacks. Similarly, unsupervised children may spend a great deal of time indoors, perhaps due to their parents’ safety concerns, watching television or playing video games rather than engaging in more active outdoor pursuits.
Alternatively, the increase in working mothers may have no adverse effect on childhood weight problems. Any correlation between working mothers and overweight children may be spurious, if, for example, mothers who work are those who would be less attentive to their children’s nutrition and exercise in any case. There may even be a negative impact of maternal work on children’s probability of being overweight if households where the mother works have more money with which to purchase more healthful meals. Similarly, children of these households may be more likely to participate in after-school sports, thereby increasing their activity levels. Even if working mothers lead to more overweight children, increases in maternal work may be a small component of the myriad environmental changes affecting children’s health. The United States might have faced the current epidemic in childhood weight problems, even if women’s labor force activity had not dramatically increased.
The purpose of this paper is to explore whether the observed coincident rise in maternal employment and childhood weight problems represents a causal relationship between these two phenomena. We focus on the role of maternal employment rather than parental employment more generally for three reasons. First, it is mothers’ labor supply that has changed dramatically over recent decades. Second, despite the dramatic increase in women’s paid market employment, they still bear the bulk of responsibility for child rearing. Third, data limitations in the analysis reported below only enable us to link children’s outcomes to employment histories of mothers.
Using the National Longitudinal Survey of Youth (NLSY), we first document a simple correlation between maternal employment and the probability that a child is overweight. The remainder of the paper attempts to identify whether this simple relationship is causal. To this end, five techniques are employed. First, we estimate probit models including a full range of observable characteristics of the mother and child. Second, we estimate “long difference” models that compare changes in child overweight status at the beginning and end of the panel to changes in maternal work history, thus differencing out any unobserved child-specific fixed effect. We also estimate sibling difference models, both comparing weight outcomes for siblings at the same time and at the same age, thus differencing out any unobserved family-specific fixed effects. Finally, we estimate instrumental variables models.
We also estimate the models by income, maternal education, and race/ethnicity. We analyze subgroups separately since public policy may interact with children’s weight in different ways for different groups. For example, if maternal work is particularly deleterious for weight problems among poor children, one might worry that welfare reform and its attendant work requirements will have unintended adverse consequences for childhood obesity.
Our results lead us to several conclusions. First, mothers who work more intensively, in the form of more hours per week over the child’s life, are significantly more likely to have an overweight child. There is no evidence that mothers who work are simply those who are inherently less attentive to their children’s weight outcomes. In other words, we do not find any support for the notion that these differences are driven by unobservable heterogeneity. Interestingly, the aggregate relationship is entirely driven by the relationship between maternal work and children’s weight outcomes among higher socioeconomic status families, despite the fact that these children are the least likely to have weight problems. For example, if the mother in a top income quartile family works an extra 10 hours per week (averaged over the weeks she worked since the child’s birth), the child is between 1.3 and 3.8 percentage points more likely to be overweight. Thus, for high socioeconomic status families, increases in mothers’ average weekly hours of work over the last three decades can explain between 12 and 35% (depending on the specification and under certain assumptions) of the increase in the fraction of children who are overweight. Finally, while our results indicate that maternal employment has a significant impact on the probability that a child is overweight for some groups, those who would blame maternal employment for the deterioration in children’s health overall need to look elsewhere for the whole story. Particularly for the subpopulations for which childhood obesity is most prevalent, mothers’ employment does not appear to be a factor.
Section snippets
Previous research
Being overweight as a child has both immediate consequences and long-term implications for individuals, as well as for society as a whole. For example, the increase in overweight children has been accompanied by a marked increase in the number of children developing type II diabetes, which has serious health risks (Thompson, 1998). In addition, studies have shown that overweight children are much more likely to become overweight adults than normal weight children (Bouchard, 1997, Dietz, 1997).
Data and descriptive statistics
To conduct our analysis, we mainly use the matched mother–child data from the NLSY, which are described briefly here and in more detail in Appendix A. The NLSY first surveyed 12,686 individuals, of whom 6283 were women, between the ages of 14 and 22 in 1979 and has continued to survey them annually through 1994 and biennially since then. Beginning in 1986, the children of those women have been surveyed biannually as well. At the time we began this project matched data through 1996 had been
Econometric approaches
Although the descriptive statistics in Table 1 make a compelling prima facie case that there is a relationship between maternal work and childhood weight problems, particularly for higher socioeconomic status groups, mothers who work are likely to differ from mothers who do not in both observable and unobservable ways. These omitted variables may bias (either up or down) the relationship between maternal work and children’s overweight status across all subgroups. In our analysis, we use five
Probit analysis
The first column of Table 2 presents the result of estimating a simple probit on the probability of a child being overweight, based on average hours worked per week (if working) and average weeks worked per year, over the child’s lifetime.
Discussion
Intuitively, one might have thought that higher socioeconomic status mothers would be those for whom working would matter least, because they are the mothers in the best position to purchase high quality child care in their absence. Instead, we find that it is only for this group that mother’s work matters, implying that when these mothers spend more time per week with their children, they are doing something that promotes a nutritious diet and exercise for their children.
There are alternative
Summary and conclusions
The contribution of this work is several fold. First, much of the research on childhood weight problems reports simple correlations between overweight status and various characteristics of the child or the family. This research is among the first to grapple with issues of causality. It presents robust evidence of a positive and significant impact of maternal work on the probability that a child is overweight. It is not simply that mothers who work are those who would have overweight children
Acknowledgements
We would like to thank Kate Baicker, David Card, Anne Case, Jon Gruber, Luojia Hu, Anna Paulson, and Doug Staiger, for helpful discussions, two anonymous referees for their comments and seminar participants at Princeton University, Harvard University, Dartmouth College, George Washington University, the University of California at Davis, the University of Chicago, the University of Illinois-Chicago, the University of Illinois at Urbana-Champaign, The Federal Reserve Bank of Chicago, and the
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