Emily Oster

7 min Read Emily Oster

Emily Oster

Do Fitness Trackers Make You Walk More?

Some research suggests "yes," but what does the data mean?

Emily Oster

7 min Read

I’m queueing up a few new COVID posts: antigen testing, the new UK variant, the question of whether you can see people freely once vaccinated, etc. And of course I’ll keep you updated as new information comes up on kids, vaccines, pregnancy and so on. But: in honor of my first real post of the New Year, I’m flashing to what could have been, in the absence of COVID-19. That is, a newsletter about new studies, what they tell us (or don’t), served with a side of econometrics.

Today: Fitness trackers.

New Years often comes with resolutions and, for many, these surround fitness: diet, exercise, some commitment to working off the excesses of December. In a non-pandemic year, gyms run full steam ahead in January, with the surge tailing off mid-February (post-Valentines slump). As part of the fitness push — especially in the absence of gyms — I suspect many people will turn to some type of activity tracker. Activity trackers tell you, broadly, how much you are moving in a given day. They’re often set up to count steps. And many people hope such a device can help them hit that magical (but totally made up) 10,000 step a day target.

Question: Will a device really help you walk more?

Recent research may suggest yes. In early December, the British Journal of Sports Medicine published a study — a meta-analysis — which combined a evidence from 28 randomized trials including a total of about 7,500 people. The trials evaluated the impacts of activity trackers (plus, in many cases, other reminders or supports) on number of steps taken. On average, studies found a moderate increase in steps: treatment group members took about 1850 more steps per day than the control. The effects were larger when combined with text messages or other reminders.

Broadly, this is good news for trackers. Of course, there are quibbles about these results. Most of the study participants (75%) were men, for example; and most of the studies followed them for only a few weeks or months. There’s also some lack of consistency across interventions. BUT: what makes this evidence compelling is that the studies are randomized.

I complain a lot about non-randomized data. A study of fitness trackers with non-randomized data would be worthless. Of course people who own fitness trackers walk more, but this basic comparison wouldn’t be helpful given the other differences across groups. Randomized data is much better; by taking a bunch of people without trackers and randomly picking half of them to get the trackers, you can be (more) confident that any differences across groups are due to the tracker.

Is that the whole story then? Should you definitely get a tracker so you can get that (average) of 1850 extra steps each day? Or: if you’re a doctor and thinking about how to motivate your sedentary patients, should you prescribe them an activity tracker?

Despite this evidence, I think it’s not so clear. Here’s where the slightly subtle econometrics comes in. When you run a randomized trial, you are able to estimate a causal effect for the people in the trial. If those people are, themselves, a random sample of the overall population then your causal effect in your trial is the correct causal effect for the overall population.

But: what if the people in your trial are not a random sample? Let’s imagine, for example, that the way you recruit people for your fitness tracker trial is by putting up signs in the subway inviting people to enroll. Who is going to want to be in your trial? One (likely) possibility is that you’ll get a disproportionate number of people who are interested in trying to walk more. This desire to walk more is what attracted them to your subway sign.

So, now, you’ll take this non random sample of the overall population and you’ll run your randomized trial on them. You’ll get a causal effect for the people in the trial. But is it the same effect you’d expect in the overall population? The answer is: it depends.

In some cases, we expect a treatment to have the same effect on everyone. Let’s say instead of evaluating the effect of activity trackers on count of steps, you were evaluating whether hitting people in the shin with a stick really hard gives them a bruise. That’s the treatment: hitting people in the shin. The impact of this treatment is likely to be basically the same for everyone. With a few exceptions, nearly everyone will bruise if they are hit hard in the shin with a stick. So, you’d get the overall right answer to your question even if the people who agreed to be in your trial were kind of unusual (which they probably would be!).

In econometric terms, we’d call this a homogenous treatment effect. The treatment effect is the same for everyone. Therefore, even if your treatment group is a non-random sample, you’re fine using it to learn about the whole population.

However, in many cases we think there are heterogenous treatment effects, meaning that the effect is not the same for everyone. And then we can be in trouble. In the particular case of activity trackers, it’s easy to imagine that the people who sign up to e be in these studies are motivated to use the tracker. They may have a larger treatment effect than random people from the population. The effects in these randomized trials would, then, overstate the overall population effects. (They could also understate them, for example if the control group without the trackers were motivated in other ways. If you want to really nerd out on this I have a paper on how one might figure out if the effects are larger or smaller in the trail population than the overall population).

In the particular setting of this meta-analysis, my guess is that the treatment effects in the studies are larger than what you’d get in the overall population. That is to say: if doctors randomly handed out fitness trackers to people, I would not expect an increase of 1850 steps on average. A lot of people would leave the trackers in their nightstands and never put them on.

Having said that: if you yourself are motivated to get a tracker, then the effects estimated in the study may be more relevant to you. It really depends on the question we are asking or, rather, who we are asking it about.

Broader point about trackers and randomized trials

This point is broader than this example. It comes up in thinking about the general conclusions of virtually any randomized trial. There is no question that we learn more from randomized trials than from observational data, but they aren’t a panacea.

There is, of course, always a COVID connection. If you look at much of the discussion around the vaccine trials, there was a lot of emphasis on enrolling a diverse group in the trials and, in particular, making sure that there was representation from communities of color who have been harder hit by by the virus. One reason for this was the concern that the treatment effect of the vaccine — its efficacy — would be different for different groups. If you tested the vaccine only in white men aged 35 to 45, and it turned out that the effect was very different in Black men, or in women, or in older people, your results wouldn’t be very helpful in predicting the overall impacts of the vaccine in the population.

Fortunately, the vaccines we have do seem to be similarly effective across a wide range of groups. Now all we have to do is actually vaccinate people.

P.S.

Yes, I have a tracker watch. It’s a Garmin Forerunner 45. I like it! I mostly use it for running but it does apparently also track steps. Current daily count: 17,369.

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Bug season is upon us. Besides annoyance, this can bring up safety concerns, particularly with ticks. They are carriers of diseases, most notably Lyme disease. So what’s the best course of action?

Prevention is key! I suggest:
⭐ Regular tick checks
⭐ Using bug sprays with DEET 
⭐ Wearing long sleeves and pants in the woods

Some parents worry about DEET, but repellants with up to 30% DEET are recommended by both the CDC and AAP. The data says you’re in the clear, so go for it. Enjoy your summer!

#parentdata #emilyoster #tickseason #bugbites #bugspray

Bug season is upon us. Besides annoyance, this can bring up safety concerns, particularly with ticks. They are carriers of diseases, most notably Lyme disease. So what’s the best course of action?

Prevention is key! I suggest:
⭐ Regular tick checks
⭐ Using bug sprays with DEET
⭐ Wearing long sleeves and pants in the woods

Some parents worry about DEET, but repellants with up to 30% DEET are recommended by both the CDC and AAP. The data says you’re in the clear, so go for it. Enjoy your summer!

#parentdata #emilyoster #tickseason #bugbites #bugspray
...

The list of what not to do while pregnant feels longer than a CVS receipt. At ParentData, we want to empower you to make the right decisions for you. 

What an amazing group of women, and an honor to speak at the #MomsFirstSummit debunking parenting myths. 

What are some pregnancy rules you chose to bend after being empowered by data?

#emilyoster #parentdata #pregnancyproblems #pregnancymyths

The list of what not to do while pregnant feels longer than a CVS receipt. At ParentData, we want to empower you to make the right decisions for you.

What an amazing group of women, and an honor to speak at the #MomsFirstSummit debunking parenting myths.

What are some pregnancy rules you chose to bend after being empowered by data?

#emilyoster #parentdata #pregnancyproblems #pregnancymyths
...

Looking for Memorial Day Weekend plans? Might be the perfect time to give potty training a shot. Potty training is notoriously difficult, and we unfortunately don’t have a lot of evidence-based guidance on what works best. So I asked the ParentData community to fill out a survey and share their knowledge — about 6,000 people responded.

👉Comment “Link” for a DM to an article that summarizes all of the best potty training advice we collected. 

Remember, you are not alone in the potty training struggle! It can be incredibly challenging, so please give yourself some grace.

#emilyoster #parentdata #pottytraining #pottytrainingtips #toddlertips

Looking for Memorial Day Weekend plans? Might be the perfect time to give potty training a shot. Potty training is notoriously difficult, and we unfortunately don’t have a lot of evidence-based guidance on what works best. So I asked the ParentData community to fill out a survey and share their knowledge — about 6,000 people responded.

👉Comment “Link” for a DM to an article that summarizes all of the best potty training advice we collected.

Remember, you are not alone in the potty training struggle! It can be incredibly challenging, so please give yourself some grace.

#emilyoster #parentdata #pottytraining #pottytrainingtips #toddlertips
...

We’re hiring an Associate Editor at ParentData! More details at my link in bio. Please share with the great writers and data-loving people in your network. 📊💻

We’re hiring an Associate Editor at ParentData! More details at my link in bio. Please share with the great writers and data-loving people in your network. 📊💻 ...

Do you brand things a certain way to get your kid to accept it? Like calling carrots “rabbit popsicles”? Or telling them to put on their “super speed socks” in the morning? Share your rebrands in the comments below! You never know who you might be helping out 👇

#emilyoster #funnytweets #relatabletweets #parentingjokes #kidssaythedarndestthings

Do you brand things a certain way to get your kid to accept it? Like calling carrots “rabbit popsicles”? Or telling them to put on their “super speed socks” in the morning? Share your rebrands in the comments below! You never know who you might be helping out 👇

#emilyoster #funnytweets #relatabletweets #parentingjokes #kidssaythedarndestthings
...

Have you ever panic-googled a parenting question when everyone else is asleep? If so, you’re not alone. 

Today is the first episode of a new biweekly series on my podcast: Late-Night Panic Google. On these mini-episodes, you’ll hear from some familiar names about the questions keeping them up at night, and how data can help. First up: @claireholt!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #emilyoster #claireholt #parentingstruggles #parentingtips #latenightpanicgoogle

Have you ever panic-googled a parenting question when everyone else is asleep? If so, you’re not alone.

Today is the first episode of a new biweekly series on my podcast: Late-Night Panic Google. On these mini-episodes, you’ll hear from some familiar names about the questions keeping them up at night, and how data can help. First up: @claireholt!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #emilyoster #claireholt #parentingstruggles #parentingtips #latenightpanicgoogle
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Sun safety is a must for all ages, especially babies! Here are my tips for keeping your littlest ones protected in the sunshine:
☀️ Most importantly, limit their time out in hot weather. (They get hotter than you do!)
☀️ Keep them in the shade as much as possible when you’re out.
☀️ Long-sleeve but lightweight clothing is your friend, especially on the beach, where even in the shade you can get sunlight reflecting off different surfaces.
☀️ If you want to add a little sunscreen on their hands and feet? Go for it! But be mindful as baby skin tends to more prone to irritation.

Comment “Link” for a DM to an article on the data around sun and heat exposure for babies.

#sunsafety #babysunscreen #babyhealth #parentdata #emilyoster

Sun safety is a must for all ages, especially babies! Here are my tips for keeping your littlest ones protected in the sunshine:
☀️ Most importantly, limit their time out in hot weather. (They get hotter than you do!)
☀️ Keep them in the shade as much as possible when you’re out.
☀️ Long-sleeve but lightweight clothing is your friend, especially on the beach, where even in the shade you can get sunlight reflecting off different surfaces.
☀️ If you want to add a little sunscreen on their hands and feet? Go for it! But be mindful as baby skin tends to more prone to irritation.

Comment “Link” for a DM to an article on the data around sun and heat exposure for babies.

#sunsafety #babysunscreen #babyhealth #parentdata #emilyoster
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I’m calling on you today to share your story. I know that many of you have experienced complications during pregnancy, birth, or postpartum. It’s not something we want to talk about, but it’s important that we do. Not just for awareness, but to help people going through it feel a little less alone.

That’s why I’m asking you to post a story, photo, or reel this week with #MyUnexpectedStory and tag me. I’ll re-share as many as I can to amplify. Let’s fill our feeds with these important stories and lift each other up. Our voices can create change. And your story matters. 💙

#theunexpected #emilyoster #pregnancycomplications #pregnancystory

I’m calling on you today to share your story. I know that many of you have experienced complications during pregnancy, birth, or postpartum. It’s not something we want to talk about, but it’s important that we do. Not just for awareness, but to help people going through it feel a little less alone.

That’s why I’m asking you to post a story, photo, or reel this week with #MyUnexpectedStory and tag me. I’ll re-share as many as I can to amplify. Let’s fill our feeds with these important stories and lift each other up. Our voices can create change. And your story matters. 💙

#theunexpected #emilyoster #pregnancycomplications #pregnancystory
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OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

Is side sleeping important during pregnancy? Comment “Link” for a DM to an article on whether sleep position affects pregnancy outcomes.

Being pregnant makes you tired, and as time goes by, it gets increasingly hard to get comfortable. You were probably instructed to sleep on your side and not your back, but it turns out that advice is not based on very good data.

We now have much better data on this, and the bulk of the evidence seems to reject the link between sleep position and stillbirth or other negative outcomes. So go ahead and get some sleep however you are most comfortable. 💤

Sources:
📖 #ExpectingBetter pp. 160-163
📈 Robert M. Silver et al., “Prospective Evaluation of Maternal Sleep Position Through 30 Weeks of Gestation and Adverse Pregnancy Outcomes,” Obstetrics and Gynecology 134, no. 4 (2019): 667–76. 

#emilyoster #pregnancy #pregnancytips #sleepingposition #pregnantlife

Is side sleeping important during pregnancy? Comment “Link” for a DM to an article on whether sleep position affects pregnancy outcomes.

Being pregnant makes you tired, and as time goes by, it gets increasingly hard to get comfortable. You were probably instructed to sleep on your side and not your back, but it turns out that advice is not based on very good data.

We now have much better data on this, and the bulk of the evidence seems to reject the link between sleep position and stillbirth or other negative outcomes. So go ahead and get some sleep however you are most comfortable. 💤

Sources:
📖 #ExpectingBetter pp. 160-163
📈 Robert M. Silver et al., “Prospective Evaluation of Maternal Sleep Position Through 30 Weeks of Gestation and Adverse Pregnancy Outcomes,” Obstetrics and Gynecology 134, no. 4 (2019): 667–76.

#emilyoster #pregnancy #pregnancytips #sleepingposition #pregnantlife
...

My new book, “The Unexpected: Navigating Pregnancy During and After Complications” is available for preorder at the link in my bio!

I co-wrote #TheUnexpected with my friend and maternal fetal medicine specialist, Dr. Nathan Fox. The unfortunate reality is that about half of pregnancies include complications such as preeclampsia, miscarriage, preterm birth, and postpartum depression. Because these are things not talked about enough, it can not only be an isolating experience, but it can also make treatment harder to access.

The book lays out the data on recurrence and delves into treatment options shown to lower risk for these conditions in subsequent pregnancies. It also guides you through how to have productive conversations and make shared decisions with your doctor. I hope none of you need this book, but if you do, it’ll be here for you 💛

#pregnancy #pregnancycomplications #pregnancyjourney #preeclampsiaawareness #postpartumjourney #emilyoster

My new book, “The Unexpected: Navigating Pregnancy During and After Complications” is available for preorder at the link in my bio!

I co-wrote #TheUnexpected with my friend and maternal fetal medicine specialist, Dr. Nathan Fox. The unfortunate reality is that about half of pregnancies include complications such as preeclampsia, miscarriage, preterm birth, and postpartum depression. Because these are things not talked about enough, it can not only be an isolating experience, but it can also make treatment harder to access.

The book lays out the data on recurrence and delves into treatment options shown to lower risk for these conditions in subsequent pregnancies. It also guides you through how to have productive conversations and make shared decisions with your doctor. I hope none of you need this book, but if you do, it’ll be here for you 💛

#pregnancy #pregnancycomplications #pregnancyjourney #preeclampsiaawareness #postpartumjourney #emilyoster
...

We are better writers than influencers, I promise. Thanks to our kids for filming our unboxing videos. People make this look way too easy. 

Only two weeks until our book “The Unexpected” is here! Preorder at the link in my bio. 💙

We are better writers than influencers, I promise. Thanks to our kids for filming our unboxing videos. People make this look way too easy.

Only two weeks until our book “The Unexpected” is here! Preorder at the link in my bio. 💙
...