By Eliza Berman
April 26, 2019

It is often said that babies don’t come with instruction manuals, but parenting advice is hardly difficult to come by. On the contrary, there’s so much of it — from John Locke to Dr. Spock, no fewer than 50,000 books for sale on Amazon and that no pressure, but I’m totally judging you mom in your postnatal-yoga class — it can feel impossible to know what the right decision is at any given juncture. And there are so many junctures.

Emily Oster, an economist at Brown University who focuses on health economics, has set out to make these decisions a little easier for parents by arming them with data and a healthy understanding of the principles of economics-driven decision-making. Her 2013 book, Expecting Better: Why the Conventional Pregnancy Wisdom is Wrong and What You Really Need to Know, has become something like a bible that gets tattered as it’s passed from friend to pregnant friend. In it, she offers digestible conclusions from reliable research and debunks myths on everything from alcohol and caffeine consumption to exercise and bed rest. Her new book, Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool, takes a similar approach with the first three years following birth.

Oster’s aim is not to provide the answer to parents’ questions about breastfeeding, circumcision, sleep and childcare. Instead, she argues that there is often more than one right answer, and it falls somewhere in between what the data says and what works for each family’s unique circumstances.

Oster spoke to TIME—with a brief pause to coordinate with her nanny—about the problem with the phrase “studies say,” whether breastfeeding is as beneficial as people say it is and how to combat that relentless parental judgment.

An economist isn’t the first person you’d expect to get parenting advice from. How did you decide to apply that framework to this subject?

I got pregnant. I started using a lot of the decision-making and data-analysis tools I use in my job to make choices about my pregnancy and then my parenting.

Women are often starved to talk about topics like pregnancy and breastfeeding. After you published Expecting Better, did people begin confiding in you?

Yes. I particularly hear a lot from women about things they struggle with, like miscarriages. I think I do sometimes serve as a repository for some of those things that people are uncomfortable talking about, even with people they’re close to, either because it’s a secret or it’s embarrassing.

When you were deciding what to cover in Cribsheet, in which areas did parents seem the most desperate for answers?

People are very starved for answers on breastfeeding and want to know how big a deal it is. They were also starved for answers on the how-tos of breastfeeding. The other place is sleep. It can be hard to get good answers about co-sleeping or sleep training or should your baby be in your room. And it feels so important, because you are so very tired.

Did you look at the evolution of parenting advice throughout history?

I did look back at what my mother and grandmother [read], which was an interesting window into breastfeeding in particular. You can see this evolution from saying, in the ‘40s, “This is a sort of primitive thing, which mostly you’re not going to do,” to in the ‘80s, “Well, you might try it, some people like it,” to where we’ve gotten now, with very extreme claims about the benefits.

You find some evidence supporting the benefits, but not an overwhelming amount. Should hospitals put so much energy into promoting it?

It is a good idea to provide support to women who want to breastfeed, and we don’t provide as much as we should. You’re telling people, “You have to do this,” and then, “Don’t take your breast out in public.” But many women feel pressure and shame if they don’t want to breastfeed or if it doesn’t work. Misleading people about the size of the benefits, which only adds to that shame, is not good.

You write about topics of heated debate like vaccines and circumcision. Do you get hate tweets shooting the messenger for delivering the data?

I certainly got some with Expecting Better. I expect I will get more of it. There are relatively few things—vaccinations is an exception—where I say, I think the right decision is x, because in most cases the best decision involves taking into account the preferences and constraints of the family. I still expect a lot of angry tweets.

Data can help us make better decisions if we want to, but even when the data exists, many people find flawed data that suits their own biases. What can economists do if people refuse to heed the data?

One of my least favorite phrases is “studies say” because you can always find a study that says whatever is the thing that you think already. And one of the things I try to do here is not what does a study say but what do all the studies say. But if, in the face of evidence on something like vaccines, people are still not listening, then I think economists would also think about how to deal with policy in those settings. One solution is to use more of a stick approach and try to enforce some particular behavior.

Truth itself feels slippery these days. Is there a parallel between parents wanting to believe their way is right and people wanting to believe their political views are right?

There’s this idea about motivated reasoning, more in psychology than in economics. You adapt the evidence to support your view. People do that in politics and they do it here for the same reasons — people really care, and they want to make the right decision and to have made the right decision. It’s hard to admit, I made the wrong choice, or it didn’t matter, there are a lot of right choices.

One could summarize this book by saying, “A lot of the things people think are bad are not that bad, and a lot of the things we think are good are not that good.” Is that fair?

Part of what makes early parenting so difficult is every choice and decision seems like it is the choice that is going to make or break your kid, including very tiny things. A lot of the message of this book is, there aren’t really any decisions like that. There are many good choices. Hopefully it’ll take a little pressure off of this experience which can be quite exhausting.

Most kids turn out fine whether they’re sleep-trained using the Ferber or Weissbluth method or not at all, but parental judgment still runs rampant. Is reducing judgment a goal?

Yes. And trying to move away from the idea that the choice you made is right and therefore other people should make it, and if they don’t, they have done something bad. If we could acknowledge that families make different choices and they could all be right, that would be much healthier.

Was there anything in your research that surprised you?

When my daughter was born, I was told not to give her any peanuts for two years. It turns out not only is that not good advice, the advice should precisely be the opposite. In the interim between my two kids, we realized introducing allergens early makes kids less likely to be allergic, not more.

You address evidence on types of preschool programs, like Montessori and Waldorf. Is it a function of privilege to be able to worry about a choice like that?

I’m an economist. We know income and education buy choice, and some of the choices in this book are not accessible to everyone. I imagine a reader with more choices is going to find more here. I’m hopeful the more basic things about breastfeeding or sleeping will help a large swath of people. But you have to like data.

You write that as kids get older, it gets harder to apply data to parenting. Could you write more books in this vein?

These issues become so much more complicated and so much more child-specific. Every kid is different, and they become more different as they get older. It’s harder to think about data speaking to the questions you would have—what’s the right kind of school? Should my kid skip a grade? I’m not sure I have as much to bring to the table.

Most people don’t take economics until college, if at all. But the kinds of decision-making skills you learn about seem like they could be beneficial at a younger age. Should it be taught earlier?

Yes! Pretty much starting in elementary school [laughs]. No, I mean, I believe pretty strongly that a lot of the core ideas in economics are very helpful for decision-making in most aspects of life, not just in where should I invest my money. The challenge is that when people take economics in high school or even in college, most of what they get is how does the stock market work and what does the Fed do, which is valuable but not helpful in making decisions about your life. I have a lot of ideas about how to teach this class. They will probably never be realized.

Your parents are economists, as is your husband. Do you ever feel like you need to spend some time in the humanities department for a change of pace?

Yes. I run a program at Brown which involves a lot of undergrads who are quite interested in the humanities. I have freshman who are taking Greek and philosophy and poetry, so I get to interact a lot with them and the faculty they’re working with. It’s good to step out and be like, “Oh, there are people working on ancient Greece, that’s fun.”

When you were 2, you were the subject of a study called Narratives From the Crib, in which your parents recorded your precocious chatter to yourself in your crib. How do you feel as an adult, and as a parent, about having been a research subject as a kid?

I don’t have any strong positive or negative feelings about it. I sometimes think about, would I have done the same thing with my kids, and I think the answer is probably yes. Particularly with very little kids, I’m not sure there’s so much privacy to protect. I did think about privacy when I was writing this book, and how much about my kids do I want to put in and are they going to later be upset that I said something particular about them.

Do you believe economics-driven decision-making can lead to less fighting in a relationship?

I do, but I think it may only be because we are both economists. I think that most of the evidence suggests that talking through decisions with your partner is helpful. I’m not sure that every couple needs to communicate using solely the language of economics, even though that works fine for me, it works fine for my parents. Economists I know who are married to non-economists tell me that this is not a panacea.

The acknowledgements say, “Mom, I know this makes you nervous, but thanks for supporting it anyway.” Can you explain?

When this book comes out, some people will say, “You’re not a good parent, you’re ruining people’s lives.” I’m prepared for that and I think the book will help many people, but it really makes my mother feel bad when people say bad things about me.

She sounds like a very caring mother.

She’s a good mom.

Write to Eliza Berman at eliza.berman@time.com.

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