Covid and the “Birthday Effect”

Bapu JENA: So, my daughter turned six in December. And if you haven’t been six in a while or had a six-year-old in your house, let me just remind you. Birthdays are a big deal at this age. And as a parent, even if you don’t get sucked into spending a lot of money on presents and parties, it feels like such a big milestone when kids are little. You really want to celebrate.

FAMILY SINGING: Happy birthday to you. Yay!

And especially during this pandemic, when things were sort of strange and sad, really even on the best days, it felt even more important to try to make our daughter’s birthday special.

But, you know, how could we do that and stay safe? My wife and I, you know, we debated what to do. What would be the safest way to gather? We thought that would be to do something outside. But it’s December in Boston!

All right, so what about a party over Zoom? And, I know what you’re thinking. Those words don’t really go well together. Zoom party? For a six-year-old?

If we did that though, we’d need to do something to make it more than your average Zoom call. And that’s when we realized there was just one man for this job.

Tricky TIM: Tricky Tim is what I go by. So that’s the name I’ll stick with. Been doing magic since I was four years old.

Tricky Tim, Zoom magician extraordinaire. This guy who’s been single-handedly saving birthday parties for kids around the world during this pandemic.

TIM: When I started these, it wasn’t because I said, “Oh no, I need to make money somehow.” It was because I had to save this girl’s birthday. This girl is going to have a terrible birthday if I don’t come up with a really good show that’s going to somehow work over video. How in the world am I going to do that?

Well, he did it. I’m telling you; I’ve never seen my daughter laugh that hard. Ever. I mean, like a full-on belly laugh, the kind of laugh where you’re laughing so hard, there’s almost no sound coming out of your mouth anymore. And to be honest, it’s not even clear that oxygen transfer is occurring at that point. 

So it is possible for a Zoom party to be a smash success. But for all the people who did still gather in-person for birthday parties in 2020, just how dangerous was it?

My colleagues and I actually did some research to find out.

We’ll also hear from a public health expert about a missed opportunity in our fight against the pandemic.

And since we’re not totally out of the Covid woods yet, we’ve got some tips from Tricky Tim about making a virtual party awesome.

From the Freakonomics Radio Network, welcome to Freakonomics, M.D. I’m Bapu Jena. I’m an economist but I’m also a medical doctor. And in each episode, I’ll dissect a fascinating question at the sweet spot between health and economics.

This week: How likely were you to get Covid-19 after a family birthday party?

Mola LENGHI: New Yorkers here are waking up to new rules.

Elle THOMAS: You’ll find few people walking down Salt Lake City streets.

LIGHTFOOT: I have ordered the closure of Chicago’s lakefront.   

While all that was going on, we know that people were still gathering in their homes. And as much as life slowed down, it obviously didn’t come to a screeching halt. We are social creatures after all. Not everyone followed social distancing and shelter-in-place orders the same way. And even people who were being pretty careful, like me, still had some interactions with others.

Big events like weddings and graduation parties were mostly postponed. But for smaller gatherings, many of us probably found ourselves bending the rules just a little bit. Maybe for a special occasion with a few friends or family members. Maybe for a birthday.

My co-authors Chris Whaley, Jonathan Cantor, Megan Pera and I wanted to see if we could find a measurable link between birthday parties and Covid. Measuring the effect of birthdays could actually help us understand the effect of smaller group gatherings of any kind, really, on the spread of the virus. The kinds of gatherings with people that we know and trust, unlike a bar or a restaurant, for example.

And birthdays are actually ideal for a natural experiment. That’s something I’m always on the lookout for as an economist. A natural experiment is when something in the world provides this randomizing effect that we can analyze. And here’s why studying birthdays works so well.

First, literally everyone has a birthday. However we did or, or didn’t celebrate them, we’ve all had at least one birthday since the start of the pandemic more than a year ago. As far as variables go, that’s about as universal as it gets.

Second, birthdays are pretty random. You’re not dramatically more likely to be born at a certain time of year if you’re rich or poor, Democrat or Republican, from, let’s say, California or Kentucky.

And third, unlike a wedding or a graduation date, your birthdate and the birthdates of your family members are actually listed in some of your health data.

And that birthday data meant we had the chance to crunch some numbers. Some really big numbers. We looked at a sample of nearly three million U.S. households with employer-based health insurance. Because these are insurance data, we could see if and when someone received a medical diagnosis of Covid-19. And we could see if that Covid diagnosis came within a couple of weeks of when someone in that family had a birthday. For each week between January and November of 2020, we compared Covid-19 diagnosis rates between households with and without a birthday in the two weeks prior.

So, what did we find?

In counties with low Covid rates, we didn’t find any increased rate of infection in the weeks following birthdays. That made sense because overall transmission rates in those counties were low. But then we looked at counties that were Covid hotspots. There, the likelihood of infection in a family actually increased by about 30 percent in the two weeks following a birthday, compared with those households in the same county that did not have a birthday during the same two-week window. And the birthday effect was about three times larger for households in which a child had a birthday. It jumped from 5.8 cases per 10,000 people to 15.8 cases.

As a researcher, with the data that we had available, I can’t tell you exactly why the effect was larger for kids’ birthdays. But as a parent, I can make some pretty good guesses. First, it’s hard for parents to cancel a kid’s birthday party, right? It’s a lot easier to skip an in-person celebration for an adult. And another reason kids’ birthdays might be more of a Covid risk? If you do have an in-person birthday party for a child, it’s going to be tricky to get the kids to socially distance. And when it comes to older relatives who are at higher risk, especially grandparents, it’s hard to keep them away from a kid’s big day.

Just ahead, how did people’s politics play into all of this? And we hear from public health expert Dr. Vinay Prasad.

Vinay PRASAD: You have to count on the fact that not everyone’s going to do everything you say, not everyone’s going to do everything you wish they did.

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Now, it’s important to note that we didn’t have information on actual birthday celebrations. Remember, there’s no national database of who had a party and who didn’t. We only knew when a family member in a household had a birthday. But because birthdays are random, the only thing that should really explain why households with a birthday had higher rates of Covid-19 in the weeks following that birthday is that some fraction of those households celebrated with other people.

And how did we make sure that this kind of interesting finding wasn’t just random statistical chance and that the birthdays were actually the cause?

We tested our findings by taking the same set of people and assigning each of them a randomly generated date of birth. Basically, we picked a date out of a hat for each person and compared that fake birthday to the dates of any Covid diagnosis in their family.

And when we repeated our analysis, we no longer found a birthday effect. There was no increased transmission of Covid in the weeks following the fake birthdays, which made us confident that the birthday effect was real. Economists call this a falsification test. It’s an important way to kick the tires when you’re crunching data.

We took a closer look at the data in a few other ways too. This one might surprise you.

Political leanings of the county didn’t make a difference. We did not find that the link between birthdays and Covid-19 changed if the majority of the people in the county voted for Donald Trump or Hillary Clinton in 2016.

It also didn’t seem to matter if there was a shelter-in-place policy in effect, which makes sense, since these policies were kind of toothless to police smaller, private social gatherings.

And, for good measure, we even looked at the weather. We thought that rainy days might drive people indoors more. But turns out there was no relationship between rainfall during the week of a birthday and a Covid-19 diagnosis afterwards.

So what can we take away from these findings? I asked Dr. Vinay Prasad to weigh in.

PRASAD: I’m an associate professor here in epidemiology and biostatistics at the University of California, San Francisco, and I’m interested in oncology, medicine, health policy, and pretty much everything in between.

Researching other health research is actually one of his areas of expertise. And, yes, I recognize that is super meta.

PRASAD: I guess meta research is really concerned about the scope, the quality, and how research is done, and the incentives around research.

Full disclosure, Vinay is also an old medical school classmate of mine. But we don’t always see eye to eye. And that’s not just because he is a little bit shorter. Maybe he’ll need some gauze for that burn.

Anyway, Vinay has been steeped in the conversations about public health during this pandemic. Here’s what he had to say about my team’s study.

PRASAD: It’s one of those studies that makes you smile because it’s a clever approach to a problem. I believe the effect they found is a real effect and I believe they really found why.

Did the results surprise him? Not really.

PRASAD: If your goal is to have sort of a sustained and reasonable pandemic response, to some degree, you have to count on the fact that not everyone’s going to do everything you say, not everyone’s going to do everything you wish they did. People are people.

And Vinay says remembering that simple fact may have improved our response to the pandemic.

PRASAD: I think appreciating that people are primates and primates have needs has to be a part of any sort of public health response. That might’ve been a missed opportunity of the pandemic. When it comes to important life events, like a child’s birthday, people want to celebrate those events. And so, the strict thing is to say, “You can’t do that.” Another strategy might’ve been to say, “Maybe there are ways you can do that more safely.”

So maybe a blanket order to stay at home, or not gather, no matter the occasion, just wasn’t realistic enough.

And maybe now that we have the data on how risky even smaller group gatherings can be, that’ll help us make better decisions too. Because I think our study also teaches us that we may not be as good at assessing the risks around us as we might think or hope.

Most people would probably think that interacting with others that they don’t know, like in a bar or a restaurant, might confer a greater risk, because you just don’t know who’s surrounding you.

But small gatherings with people we know and trust could pose a different problem. We let our guards down a little bit more. I know I certainly have. I mean, I would wear a mask if I went to the store, but, you know, if a friend came over, would I always have a mask on inside? I mean, I tried to, but I don’t know that I always did.

Our study also doesn’t speak at all to what’s good or bad, right or wrong, but it does help quantify the tradeoffs that exist. And it’s up to all of us to figure out what do we do with that better understanding of risk. And to decide whether to adapt our behavior.

Speaking of adapting, I want to give the final words to Tricky Tim, the magician who made it cool to tell your friends to stay home on your birthday and to log onto Zoom instead.

Back in early 2020 when Covid first started spreading, his in-person gigs were all getting canceled. Then he got a message from a former client.

TIM: Isabel’s birthday is coming up. Do you think you could do a Zoom magic show? From the very start, the motivation was to save Isabel’s birthday.

Since that first party for Isabel, he’s performed hundreds of virtual shows for people all over the world during the pandemic. Early on, Tricky Tim was careful to scope out the competition.

TIM: One thing that didn’t work, and this is going to sound silly, but trying to do magic. So if all you did was say, “Watch me do this,” um, it’s boring! You know, I, I saw this guy do a fantastic rope routine where, I mean onstage, if you’re right there watching it, you go, that’s impossible. That’s cool. On video? It was just boring.

So Tim packed his show with visual jokes and made it as interactive as possible for the kids watching. Word spread that he was the guy to go to if you wanted to do a Zoom magic show. And suddenly his schedule was intense.

TIM: Busiest week was 37 shows in one week. The most shows I did in a day was eight shows in a day. So, I think I started the first one at five in the morning. I’d do 5:00 a.m. shows for Ireland. And then 11 o’clock at night would be like the Philippines or Australia.

But the most grueling part of his work might feel familiar to a lot of us. 

TIM: The hardest part was not the shows. I have the energy to do the shows. That’s no problem. Hardest part is keeping up with the emails. I couldn’t. It was too much.

I hear you about too many emails, Tricky Tim. I hear you. Thankfully, things are calming down a little bit now. Fewer people are booking virtual shows as people get vaccinated and venture back to in-person parties. And while Tricky Tim has been able to get back on stage, he also thinks there may still be some appeal for a virtual birthday party even after the pandemic.

TIM: How else could Tyler’s seventh birthday have every single person he knows on the planet be at his party? The only way you can do that is at a virtual show, you know?

That’s it for this week’s episode of Freakonomics, M.D. Thanks for listening, and I hope you’ll subscribe or follow the show. I’ll be digging into a different study each week to uncover the hidden side of healthcare. Sometimes they’ll be studies that my colleagues and I have done, like today. Other times we’ll focus on the discoveries of other researchers, and we’ll hear from them too. Everything from the unexpected things we’re learning from the pandemic to what grocery store prices and heart surgery have in common.

Coming up next week: How much does having good information affect your health? And what if the patient is a doctor too?

If you have any thoughts on the show, ideas, anything at all, I’d love to hear from you. You can email me at bapu@freakonomics.com. 

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Freakonomics, M.D. is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, No Stupid Questions, and People I (Mostly) Admire. This show is produced by Stitcher and Renbud Radio. You can find us on Twitter and Instagram at @drbapupod. This episode was produced by Tricia Bobeda and mixed by Adam Yoffe. Original music in this episode was composed by Andrew Edwards. Our staff also includes Alison Craiglow, Greg Rippin, Joel Meyer, Emma Tyrrell, Lyric Bowditch, Jasmin Klinger and Jacob Clemente. If you like this show or any other show in the Freakonomics Radio Network, please recommend it to your family and friends. That’s the best way to support the podcasts you love. As always, thanks for listening.