Analysis & Comment

Opinion | The Data ‘Bad Moms’ Need

In 1980, 8.6 percent of first births were to women over 30; by 2015 this was 31 percent. This is more than an interesting demographic fact. It means that many of us are having children much later than our parents did. By the time a baby arrives, many of us have been through school, spent time in the working world, developed friendships, hobbies. And through all of these activities, we have probably grown used to the idea that if we work harder — at our jobs, at school, at banking that personal record in the half marathon — we can achieve more.

Babies, however, often do not respond to a diligent work ethic. Take, as an example, crying.

When my daughter, Penelope, was an infant, she was typically inconsolable between 5 and 8 p.m. I’d walk her up and down the hall, sometimes just crying (me crying, that is — obviously she was crying). I once did this in a hotel — up and down, up and down, Penelope screaming at the top of her lungs. I hope no one else was staying there. I tried everything — bouncing her more, bouncing her less, bouncing with swinging, bouncing with nursing (difficult). Nothing worked; she would eventually just exhaust herself.

I wondered whether this was normal. I’m an economist, someone who works with data. I wrote a book on using data to make better choices during pregnancy; it was natural for me to turn to the data again once the baby arrived.

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And here, faced with crying, I found that the data was helpful. We often say babies are “colicky,” but researchers have an actual definition of colic (three hours of crying, more than three days a week, for more than three weeks) and some estimates of what share of babies fit this description (about 2 percent). But the same data can also tell us that many babies cry just a bit less than that, and almost 20 percent of parents report their baby “cries a lot.” So I was not alone. The data also told me the crying would get better, which it eventually did.

But I also found, more so than in pregnancy, that there are limits to the utility of general information. Parenting is full of decisions, nearly all of which can be agonized over. You can and should learn about the risks and benefits of your parenting choices, but in the end you have to also think about your family preferences — about what works for you.


Take breast-feeding. When I was pregnant and I imagined myself breast-feeding, I usually pictured myself out to brunch with some friends. When the baby was hungry I’d pop on my color-coordinated nursing cover, and she’d latch right on while I enjoyed my mascarpone French toast.

This is not what it was like at all. Like many women, I found breast-feeding incredibly hard. I have one particularly vivid memory of trying to nurse my screaming daughter in a 100-degree closet at my brother’s wedding.

These struggles are made worse by the societal, familial and medical testimonies to the many benefits of breast-feeding. Here, for example, is a partial list of supposed benefits to breast-feeding, culled from medical sources and less official parenting resources: smarter babies with less diarrhea and asthma, fewer ear infections, and a lower risk of obesity and diabetes, and thinner, happier moms with better friendships.

Better friendships? Don’t get me wrong — motherhood can be lonely and isolating, and meeting other moms is a great idea. That’s what stroller yoga is for. But I’m hard-pressed to figure out which of my friendships were enhanced by my attempts to feed a screaming baby in a closet.

Many of the benefits cited here do, however, have some basis in evidence, just not always especially good evidence. And even when the evidence is good, the benefits are smaller than many people realize. This is where being an economist comes in handy.

Most studies of breast-feeding are biased by the fact that women who breast-feed are typically different from those who do not. In the United States, and most developed countries, more educated and richer women are more likely to nurse their babies. This is the result of a host of factors, chief among them a lack of universal maternal supports.

Having more education and resources is, of course, linked to better outcomes for infants and children independent of breast-feeding. This makes it very difficult to establish the causal effect of breast-feeding — whether, for an individual woman, nursing her baby will make the child better off.

Some of the best evidence on breast-feeding comes from the Promotion of Breast-Feeding Intervention, or Probit, study, a large randomized trial from the 1990s run in Belarus, in which some of the mothers received breast-feeding guidance and support and some didn’t. Based on this data, the most well-supported benefits of breast-feeding are lower risks of gastrointestinal infections (with symptoms like diarrhea or vomiting) and of rashes and eczema early in life. To put some numbers to it, the study found that of the babies of a group of mothers encouraged to breast-feed, 9 percent had at least one episode of diarrhea, compared with 13 percent of the children of mothers who weren’t encouraged to breast-feed. The rate for rashes and eczema was 3 percent versus 6 percent.

Yet the study found no effect on respiratory infections, including ear infections, croup and wheezing. So why do we continue to see the “evidence-based” claim that breast-feeding reduces colds and ear infections? The main reason is there are many observational studies that do show that breast-feeding affects these illnesses.

For example, an observational study of nearly 70,000 Danish mothers and their children published in 2016 found that breast-feeding more than six months reduced the risk of an ear infection from 7 percent to 5 percent. This study was very careful, with excellent data that allowed the authors to adjust for a lot of differences across mothers and children.

But observational studies are less convincing than randomized trials because they have a harder time establishing causality. Should we give any weight to this evidence if we have the Probit trial?

On one hand, randomized evidence is clearly better. On the other hand, the Probit trial is only one study. If there are small benefits from breast-feeding, they might not show up as significant effects in a randomized trial, but we would still like to know about them. Given the weight of the evidence, I’d put the link between breast-feeding and a small reduction in ear infections in the “plausible” category. But there is nothing as compelling on colds and coughs.

What about long-term benefits, and the claims that breast-fed kids will grow up to be thinner, healthier and smarter? One woman told me her doctor had warned her that by quitting breast-feeding, she was costing her child three I.Q. points.

Let’s return from the land of magical breast milk to reality. Even in the most optimistic view about breast-feeding, the impact on I.Q. is small. Breast-feeding isn’t going to increase your child’s I.Q. by 20 points. How do we know? Because if it did, it would be really obvious in the data and in everyday life.

The question, really, is whether breast-feeding gives children some small leg up in intelligence. If you believe studies that just compare kids who are breast-fed to those who are not, you’ll find that it does. There is a clear correlation here — breast-fed kids do seem to have higher I.Q.s.

But again, this isn’t the same as saying that breast-feeding causes the higher I.Q. One study of Scandinavian 5-year-olds found that children who nursed longer had cognitive scores that were nearly 8 points higher on average. But their mothers were also richer, had more education and had higher I.Q. scores. Once the authors adjusted for even a few of these variables, the effects were much smaller.

In fact, the most compelling studies on this compare siblings, one of whom was breast-fed and the other not; these find no significant differences in I.Q. This same type of sibling study has also looked at obesity and, again, found little to no impact.

The good news for guilt-ridden moms is that there is little convincing evidence for any long-term effects like these. The Probit researchers followed the children in the trial through the age of 6½. They found no change in allergies or asthma, cavities, height, blood pressure, weight, or indicators for being overweight or obese.

If you’re a mother trying to decide whether breast-feeding is worth it or not, there’s one more piece of data you should take into account: the possible effects on your own health.

A lot of the claimed benefits of breast-feeding are about mothers, and many are bogus. Breast-feeding doesn’t seem to promote much additional weight loss or provide free birth control. There is no evidence linking breast-feeding and friendship quality.

However, there is real evidence base for a link between breast-feeding and cancers, in particular breast cancer. Across a wide variety of studies, there seems to be a sizable effect — perhaps a 20 percent to 30 percent reduction in the risk of breast cancer for women who breast-feed for longer than 12 months. In addition, the case for causality is bolstered by a concrete set of mechanisms. Researchers suggest that breast-feeding changes some aspects of the cells of the breast, which make them less susceptible to carcinogens.

After all that focus on the benefits of breast-feeding for kids, it may be that the most important long-term impact is actually on the health of the mother. Moms often feel selfish for thinking about their own wants and needs when faced with decisions about their kids. In this case, the data gives you permission to put yourself first for once.

Sleep Training

There are other fraught parenting decisions for which the evidence is much easier to understand than it is for breast-feeding. One example is sleep training.

Sleep training — colloquially, the “cry it out” technique — refers to any system where you leave the baby in his crib on his own at the start of the night, and sometimes let him fall back to sleep on his own if he wakes during the night. The name refers to the fact that if you do this, your baby will cry some. Pediatricians often recommend sleep training, and many parents do it.

But go on the internet, and you’ll find many articles detailing the extensive long-term damage sleep training will do to your child. At its core, the concern from the opponents of “cry it out” is that your baby will feel abandoned and, as a result, struggle to form attachments to you, and ultimately to anyone else.

This idea comes, perhaps surprisingly, from 1980s Romania, where thousands of children lived in orphanages with very little human contact for months or even years. One of the things visitors noticed in these places was the eerie quiet. Babies didn’t cry, because they knew no one would come. The argument is that “cry it out” does the same thing.

This is absurd. Sleep training methods do not leave the infant for months without any human contact, nor do they suggest subjecting children to the other types of physical and emotional abuse that occurred in those orphanages.

To learn about the impact of sleep training, we need to study it in the way it is actually used. Fortunately, many people have, and in a lot of those cases they used randomized trials.

Consider an Australian study of 328 mothers whose 7-month-old babies were having problems sleeping. Approximately half were assigned to do a sleep-training regimen, and the others were not. In the short term, the authors found significant benefits: The intervention improved sleep for children and also lowered parental depression. But they didn’t stop there.

They returned to evaluate the children a year later and five years later, when the children were 6. In this later follow-up, which included a subset of the original families, the researchers found no difference in any outcomes, including emotional stability and conduct behavior, stress, parent-child closeness, conflict or parent-child attachment. Basically, the kids who were sleep-trained looked exactly like those who were not.

These results are not an outlier. Review studies of sleep-training interventions do not find negative effects on infants. And many show sizable improvements in maternal depression and family functioning. Sleep affects mood, and parents who sleep less feel worse. The evidence paints a pretty pro-“cry it out” picture.

Nonetheless there are academic articles that argue against it. One small study that gets a lot of play shows that in the few days after sleep training, mothers are less stressed, but the same is not true of infants. The researchers interpret this as a signal that the mothers and children are losing emotional touch with each other, but this is a stretch. Why not interpret the evidence to say that cry-it-out relaxes parents without hurting children?

Fundamentally, the argument against sleep training is theoretical: that some children are devastated, even if those results don’t show up in the data, or that the damage may not manifest until babies are adults.

I think it is fair to say that it would be good to have more data. It’s always good to have more data! However, the idea that this uncertainty should lead us to avoid sleep training is flawed. Among other things, you could easily argue the opposite: Maybe sleep training is very good for some kids — they really need the uninterrupted sleep — and there is a risk of damaging your child by not sleep training.

Does this mean you should definitely sleep train? Of course not — every family is different, and you may not want to let your baby cry. But if you do want to sleep train, you should not feel shame or discomfort about that decision.

‘Working Moms’

Finally, there are some parenting decisions where the data just isn’t much help at all, and family preferences have to take the front seat. One example is the question of whether to work outside the home.

This decision is stressful. It often seems to define your whole parenting persona: What kind of mom are you? Are you a “stay-at-home mom” or, as the child of one of my friends once described her, a “stay-at-work mom”? Language like this is never helpful, and even less so when it frames this decision in such a gendered and heteronormative way. What if Dad stays home? What if there are two moms? Or only one parent?

Really, this decision could be better stated as: “What is the optimal configuration of adult work hours for your household?” Less catchy, but more helpful.

If you try to look to the evidence on what is “best” for children, you’ll be disappointed. There are studies of this, of course, but they’re hard to learn anything from, because it is extremely difficult to separate a family’s circumstances from decisions about employment. A 2008 meta-analysis found that children in families where one parent worked part-time and the other full-time performed best in school — better than children with two parents working full-time and better than those with one parent who didn’t work at all.

But again this is probably a result of many differences between those families, not just the mothers’ career decisions. There is really no compelling evidence that proves that having a stay-at-home parent affects child outcomes, positively or negatively.

(There is reliable evidence that time at home in a baby’s first few months is beneficial, but that is an argument for longer maternity leave, not for not working at all.)

This means that the decision really comes down to what works for your family. One part of this is obviously your budget, but the other part is your preferences.

I work because I like to. I love my kids! They are amazing. But I wouldn’t be happy staying home with them. It isn’t that I like my job better — if I had to pick, the kids would win every time. But the “marginal value” of time with them declines fast. (“Marginal value” will be familiar to anyone who remembers their Econ 101. There may not be any useful data on this question, but economic theory still comes in handy.) The first hour with my kids is great, but by the fourth, I’m ready for some time with my research. My job doesn’t have this nose-dive in marginal value — the highs are not as high, but the hour-to-hour satisfaction declines much more slowly.

It should be O.K. to say this. Just like it should be O.K. to say that you stay home with your kids because that is what you want to do. In our attempts to focus so much on what is best for our kids, it is a good idea to step back and think about what works for you.

And Everything Else

These decisions — breast-feeding, sleep training, working — are just three of many that will come up in the first year of a child’s life. More await, from co-sleeping to screen time and more.

One day, your child will have a temper tantrum. How on earth do you deal with that? Exorcism? And what about potty training? You many find your child is one of a surprisingly large share (about 1 in 5) who refuse to poop in the toilet (it has a name: “stool toileting refusal”). In your pre-child life, you probably never thought about the question of how to encourage someone to poop in a particular location. But there you are, needing to find your way.

That lady on the internet comment board wants to tell you what to do, but she doesn’t live in your house, and she cannot know what is right for your family.

I’m not trying to give advice. I’m just arguing that in many cases the data can be helpful. But if the data falls short and you still want advice, let me pass along something our pediatrician once told me. It was our 2-year-old’s checkup, and I had my usual list of neuroses.

“We are going on this vacation, and there are bees,” I said. “It’s kind of isolated. What if Penelope is stung? She’s never been stung before. What if she’s allergic? How will I get her to a doctor in time? Should I bring something to be prepared for this? Should we test her in advance? Do I need an EpiPen?”

In other words, I had built up this elaborate and incredibly unlikely scenario in my head. I needed someone to remind me that yes, this could happen. But so could a million other things. Parenting is not actually about planning for every possible disaster.

The doctor paused. And then she said, very calmly:

“Hmm. I’d probably just try not to think about that.”

Emily Oster, an economics professor at Brown, is the author of “Expecting Better” and the forthcoming “Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool,” from which this essay is adapted.

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