Babies are cute and cuddly — but their arrival also prompts a barrage of stressful decisions to be made fast. What’s the birthing plan? How long will you breastfeed? To sleep-train or not? Day care, nanny, or stay-at-home parent? On and on it goes.

Emily Oster, a professor of economics at Brown University, found herself overwhelmed by the decision onslaught when she had her first child. “It’s hard to be thoughtful about any one of [the choices],” she said, because there’s always another urgent parenting question waiting to be answered.

So Oster decided to tour the research on parenting in a new book, Cribsheet. Just as she did for her best-selling 2014 book on pregnancy, Expecting Better, she used her skills as an economist to parse data and create decision trees, this time to help moms and dads navigate parenthood from birth to preschool.

Once again, she’s managed to deliver something that feels fresh, even revolutionary: a tough-minded look at the science behind a slice of life where data-driven approaches are sorely lacking.

When it comes to breastfeeding, Oster finds the conventional wisdom isn’t quite accurate — and that the truth according to the research is more complicated than medical experts or other parents might suggest. With sleep training, a lot of the “wisdom” in online parenting forums is flat wrong. On the questions of whether to co-sleep with your baby or whether having kids truly hinders a couple’s happiness, the answers aren’t as black and white as many suggest.

And sometimes the evidence isn’t all that helpful. “In general, parenting issues are hard to study,” Oster told me. “Randomized controlled trials are difficult to implement, and comparing families who make different choices is fraught with problems. Having said this, there are some cases where I think the data is better.”

I asked her to walk me through three big misconceptions she discovered that most surprised her when she looked at the parenting research. Here’s what she told me.

Co-sleeping is not risk-free — but its riskiness depends on your other behaviors

The question of how parents and babies can get more sleep is one of the most charged parenting topics — particularly whether exhausted moms or dads should sleep together with their babies.

There are two sides in this debate: those who say co-sleeping is a great way to bond with baby and get a little more rest, and those who suggest co-sleeping parents are essentially murderers (because of the risk that the baby gets smothered or falls during the night). Turns out the pro-bed-sharing camp is correct here, with some caveats: When co-sleeping is done correctly, it’s not all that risky relative to many other things parents do with their kids, like driving them in cars.

“There are really big differences in how risky co-sleeping is based on your other behaviors,” said Oster. So if you’re smoking and drinking, the risk of a baby dying during co-sleeping shoots up dramatically compared to women who have the same behaviors but only share a room with their child. If you’re not smoking or drinking, there is a slightly elevated risk, but Oster said it’s “probably on the order of some of the risks you’re taking every day by putting your kid in the car.”

To be more specific, the breastfed babies of nonsmoking, non-drinking moms who co-sleep experienced 0.22 deaths per 1,000 live births, compared to 0.08 deaths among moms with the same behaviors who just shared a room (not a bed) with their child. “In the US, the overall infant mortality rate is around 5 deaths per 1,000 births,” Oster writes. “This therefore represents a very small increase relative to the overall mortality rate.”

The takeaway: While co-sleeping isn’t risk-free, if you take the right precautions, you can dramatically reduce the chances of anything bad happening to your baby. (If you’re thinking about co-sleeping, check out La Leche League’s Safe Sleep Seven for some advice on how to do it safely.)

There’s no good evidence that being a “working mom” will harm your kids

Some parents have to work to support the family. Other parents can choose to work. In both cases, guilt can often bubble up — along with concerns that your decision might harm your child in some way. The choice can be especially fraught for moms, Oster said, who feel “like it’s going to shape [their] child.”

But Oster finds we don’t have especially good evidence on this. In fact, many of the studies we have are problematic: Parents who can stay at home, or work part-time jobs, are so different from parents who don’t or can’t that it’s hard to separate out whether it’s the employment setup or family circumstances that made a difference in kids’ outcomes.

According to the data, Oster concludes, babies benefit from moms who take some maternity leave: Premature births tend to be lower, and so does infant mortality. But “these benefits seem to be mostly about outcomes in infancy (albeit extremely important ones), not about longer-term impacts.” In fact, there’s no difference in the outcomes of kids who have a stay-at-home parent versus those who don’t, she finds. So there’s no solid proof that stay-at-home parenting will benefit kids in the long term — or that the reverse is true.

“Someone claiming they’re very sure one of these choices is the best choice — that claim can’t be based on data,” she says. Instead, she suggests parents think about their preferences and their family budget rather than trying to “optimize something about your child.”

After children, your marriage is not doomed to unhappiness

You’ve probably seen them floating around: U-shaped curves of marital satisfaction, showing that a couple’s happiness plummets after having kids and only rebounds decades later, near retirement. These charts can feel like a dire warning to happy couples thinking about having babies.

But, Oster finds, who you are before you have kids heavily influences the likelihood that your marital bliss will drop off a steep happiness cliff.

“In general, people tell you that you will not be happy with your marriage after you have kids,” she said. “That’s on average true — marital satisfaction declines — but those declines are larger in some groups and in some families than others.”

In particular, people who planned their pregnancies, those with more financial resources and social support, and couples that were happier pre-children tend to see smaller and shorter declines in their happiness post-baby. “It correlates in the way you might expect with differences in socioeconomic status,” Oster said. “Part of it is that there are a lot of stresses — financial and time — that come with having a kid, and those are more acute if you don’t have other resources.”

So like a lot of the parenting info she unpacked, the idea that happiness plummets post-kids turned out to be not quite right. “It’s useful to remember,” Oster said, “that advice should be just that: advice. You can learn from what other people do, about what works for them and about the options you have. But what other people do won’t necessarily work for you, and you’ll have a happier time parenting if you make your own choices.”

Listen to Emily Oster on Ezra Klein’s podcast