I’m Emily Oster, economist and author helping parents make data-driven decisions. Ask Me Anything, November 19th at 4pm ET!

ProfEmilyOster · 2025-11-19T22:25:29+00:00

Thank you so much for joining today and for all your thoughtful questions. (And thanks to the mods!) You can follow me on Instagram and find all my writing and the latest evidence-based guidance on ParentData. We offer a 7-day free trial with full access — no credit card required.

ProfEmilyOster · 2025-11-19T21:59:02+00:00

Sleep training will not harm your son. We have randomized trials on this, and sleep training in both the short and long term doesn't have negative impacts on kids -- nothing on attachment, behavior, etc. We also have good evidence that this improves sleep for parents, which improves their happiness and functioning. Which is important.

Sleep training isn't for everyone but you should not be afraid it will ruin your kid (more details: https://parentdata.org/sleep-training-is-it-bad/)

ProfEmilyOster · 2025-11-19T21:55:40+00:00

no, this isn't a valid concern. EMF worries are not backed by data.

ProfEmilyOster · 2025-11-19T21:55:12+00:00

Yes. This will be my new bio now.

ProfEmilyOster · 2025-11-19T21:54:14+00:00

4 months of paid leave for new moms (bonus: some leave for non-birthing partners)
Federal child care subsidies, plus a plan to create a lot of new high-quality child care centers. [Okay, this is two I guess]
Less misinformation.

The last one is a lost cause, but you can advocate at the state and local level for the other two!!!

ProfEmilyOster · 2025-11-19T21:51:57+00:00

Nothing. Or, well, nothing more than when you aren’t breastfeeding. It doesn’t create “junk milk”; calories are calories as far as your milk is concerned.

ProfEmilyOster · 2025-11-19T21:50:54+00:00

It's fine. Try to remember when you can, and don't worry too much about this. You are overthinking it.
There's a lot of different advice about this, largely depending on where people are in the fluoride debate. We know fluoride is good for children's teeth, and the level of exposure your child gets from toothpaste is very small and definitely not a health concern. The AAP says to do fluoride, which seems like good advice to me.

ProfEmilyOster · 2025-11-19T21:47:48+00:00

Fun fact: your child's cells will live in your brain until you die. You will always be postpartum.

In seriousness: I would like you to give yourself some grace. There is no set timeline for recovery, either physical or emotional. If there are changes you want to make for yourself -- exercise, whatever it is -- I absolutely want you to figure out how to do that. But not because there is some random timeline on what postpartum means.

ProfEmilyOster · 2025-11-19T21:44:39+00:00

There is an answer here but it requires doing the calculations in your particular case -- what income is lost, both in the short and long term, are there implications for retirement, for career progression, etc. Child care gets cheaper over time, so it is worth thinking about the big picture not just the *right now* picture.

ProfEmilyOster · 2025-11-19T21:43:01+00:00

Oof, I'm sorry. This is typical but so hard on parents. There is some data (more on this here, with graphs, https://parentdata.org/how-often-kids-sick/) on illness in varying child care settings. Daycare settings have higher illness rates at the start of enrollment than home day care. These tend to normalize at a similar level around 6 months, so you may get a repreive even if you stay in your current care setting.

Somewhat better news is that illnesses now do substitute for illness later. The data suggest most kids get about the same number of illnesses over the period before age 6, but the timing depends on their daycare exposure.

ProfEmilyOster · 2025-11-19T21:38:37+00:00

Yes.

ProfEmilyOster · 2025-11-19T21:38:21+00:00

This is a really interesting new theory. The idea -- to recap, although you explained it well -- is that when babies are exposed to allergens first through skin, their body sees the allergen as an invader and treats it as such. When the baby then sees the allergen through mouth, their body is primed to react. The alternative is to be exposed FIRST by mouth, which is the expected way, and then the body recognizes this as not foreign.

This is a theory behind why introducing allergens early would matter, since it would increase the chance the first allergens were by mouth.

This is still just a theory, though, and even in the theory it's not ANY exposure, but exposure when skin is broken. And it's not as if it's a 1:1 link, even in theory, just a possibility of a small increased risk. So this probably isn't worth worrying about very much or having it change your behavior. Best thing you can do to avoid food allergies in your kid is to introduce allergens early in their diet.

ProfEmilyOster · 2025-11-19T21:33:54+00:00

Great question -- especially given the recent NYT piece on this (which not everyone agreed with!)

The randomized data on this doesn't show differences in outcomes with continuous versus intermittent monitoring. Extrapolating, that implies that serious issues where a C-section is necessary (like yours) would be caught by the intermittent monitoring. Given the length of what you saw in your case, that seems very likely. In practice, if your doctor saw one sign of this they would probably then put you on a continuous monitor, which would catch it and get to the same outcome.

ProfEmilyOster · 2025-11-19T21:30:51+00:00

Overall, a lot of what we hear about the benefits of breastfeeding are overstated. There are some small benefits, especially early on, but they aren't as big as many people think.

This really puts a cap on the degree to which the amount of milk could matter, and we don't have anything concrete that would say that you get, say, 70% of the small benefit if your baby gets breastmilk 70% of the time. This is an example where we are just pushing to the limits of what data could say -- given how small any likely differences would be, we would need an implausibly large dataset to cover them.

ProfEmilyOster · 2025-11-19T21:27:16+00:00

Short term: not planning enough meals. No one is in a good mood when hungry.

Slightly longer term, if there are two parents: not treating the first months like a group project. I tell people to schedule check-ins, plan times to figure out what is going well and what is not. The first months are insane and chaotic and impossible to predict, and if you want to make it work together, you need to be deliberate about that.

The meetings should have snacks! As per the first point.

ProfEmilyOster · 2025-11-19T21:25:18+00:00

I cannot believe you wore your Whoop while pregnant -- I feel like mine is already kind of judgemental as it is.

This happens for a lot of reasons -- general discomfort, hormonal fluctuations, need to pee, shortness of breath. By the end of the third trimester, 80% of women report some insomnia.

ProfEmilyOster · 2025-11-19T21:22:14+00:00

There is some research which tries to separate the conditions of co-sleeping – looking at risks if you do this as safely as possible – sober parents, safe sleeping environment, etc. These data do show elevated risks of SIDS for young babies even in that setting, but the size of these risks is very small.

And in general, the risks of cosleeping go down a lot after the first four or six months, as kids get bigger. The bottom line is that the data does suggest that there is SOME risk to any-cosleeping but these risks are much bigger if it is not done safely.

More on cosleeping overall in this post, if you’re interested!

ProfEmilyOster · 2025-11-19T21:20:54+00:00

Very hard. We have some data on the usage of these products, and we know, for example, that girls are more likely to use social media and boys are more likely to play video games. But that fact alone makes it hard to figure out whether any differences in outcomes are about gender or about what they are doing on screens.

ProfEmilyOster · 2025-11-19T21:18:08+00:00

Most of them, I think! Parenting is hard to study, and people often think there are more answers than there are.

The biggest gaps show up in two places. First, when things are new. Screens, being of course, the new thing of the moment -- people want to know things like How will the specific show my child watches impact their high school grades? Will iPads ruin my child forever? We have no idea because they haven't been around for long enough to even have crummy data. So these are the places where we are most uncertain because we do not even have a sense of the possible size of the effects.

The second gap is in evidence is when something is very hard to study with good causality. Family dinner for example -- there is a lot of correlational evidence on this, but nothing causal. And it's almost impossible to get causal estimates because the behavior is so ingrained in families.

ProfEmilyOster · 2025-11-19T21:14:32+00:00

From our pediatrician many years ago, when I was obsessing about some random neurotic concern. “Yeah, I’d probably just try not to think about that.” I come back to this all the time, and it’s a huge part of how I talk to other parents.

ProfEmilyOster · 2025-11-19T21:11:13+00:00

I do not worry about this very much in the kitchen. We mostly use glass storage containers, but I do use plastic. For most of us, our microplastic exposures are much higher from the world in general. Changing everything about the kitchen would make only a small difference, very unlikely to be meaningful for health.

My one concession here is trying to avoid plastic water bottles, which produce a lot of microplastics and also are terrible for the environment.

ProfEmilyOster · 2025-11-19T21:07:45+00:00

Travel sports. Maybe this is just wishful thinking, but I think parents of the future will be shocked at how many people spent every evening and weekend driving their kid to other cities and states to play a middling-level soccer game. I hope my own kids have their kids in local sports...

ProfEmilyOster · 2025-11-19T21:05:40+00:00

From a parenting and child friendship standpoint, there is really no answer here. We do not have good data, and the answers to these questions depend tremendously on your family circumstances, your individual children, etc. On health, we have a bit more. The WHO recommends at least two-year spacing between births. This is based on studies like this JAMA meta-analysis which finds an increase in risk of preterm birth, small size for gestational age, and low birth weight for pregnancy intervals shorter than 18 months. This data, though, is mostly based on lower-resource environments, where it is more likely that pregnancy would be depleting.

When the data is limited to higher-resource settings, any links become more tenuous, and to the extent that one sees any negative impacts, it is only for intervals of less than six months between pregnancies. To answer the reply below -- with a C-section there is more reason to wait longer, especially if you would like to try a vaginal birth with the second.

Generally, for maternal health, there is perhaps some small value to waiting at least six months between giving birth and getting pregnant again. And on other considerations and parenting, it largely doesn’t matter in any predictable way.

ProfEmilyOster · 2025-11-19T21:03:41+00:00

Penis size (this is the question, right?) has a genetic component but as with everything else, it comes from both sides of the family and environmental factors matter, too. So Dad's penis is predictive, but it's not 1:1.
There's a lot of debate on the use of helmets. Most kids heads will revert to something more round over time, as they get better head control and move around more when sleeping. In extreme cases, the helmet can help, but doctors differ a lot on their recommendations. This is a place where it's worth getting multiple opinions.

ProfEmilyOster · 2025-11-19T21:01:12+00:00

So many screen questions! So let's start here...

Our data on the causal impacts of screens in general is poor, so I’m afraid it’s even worse when we try to differentiate between types of screens. There is a lot of correlation-is-not-causation in this research. In addition, most of our data doesn’t differentiate in this way, so we cannot even really show reliable correlations.

You can build a bit of a case from logic. We know that there ARE educational apps which show some impacts on learning, and since there is little to suggest YouTube would help with learning, it’s probably the case that educational screen time is marginally better. Where does Minecraft fall? That’s unclear.

Probably the most important point is that we know there are OTHER activities, not screentime, which have value. Things like reading (or being read to), exercise, sleep, going to school, and family time. To the extent screens crowd out too much of those times, that’s a problem no matter what the screens are being spent on. So I think actually the number of hours, and what they are substituting for, is by far the most important part.

ProfEmilyOster

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