The Peltzman Effect in Children

David Ball, a professor of risk management at Middlesex University, analyzed U.K. injury statistics and found that as in the U.S., there was no clear trend over time. “The advent of all these special surfaces for playgrounds has contributed very little, if anything at all, to the safety of children,” he told me. Ball has found some evidence that long-bone injuries, which are far more common than head injuries, are actually increasing. The best theory for that is “risk compensation”—kids don’t worry as much about falling on rubber, so they’re not as careful, and end up hurting themselves more often.

From The Overprotected Kid by Hanna Rosin in the Atlantic.

Addendum: More on the Peltzman Effect.


just another example of regulation backfiring

economists cut through the crap that the liberal says will help us to give us the truth, which is that they don't help

Momma always told me to "go play in the traffic."

Who knew? She really cared.

...or it could be argued that this is a win because children can now enjoy riskier, than therefore more exciting, play without any increased likelihood of injury. The same argument can be made in favour of various other paternalistic liberal policies.

The info I saw (sorry, can't remember where) claimed that there were more off-playground injuries the more protected a playground became. So maybe Johnny gets to climb higher at the playground than he would have been able to without the rubber mat under him, but then he thinks he's bulletproof and if he ventures to climb a tree that high and falls he gets hurt, while playground-deprived Jimmy only climbed trees, got better at climbing trees, and had fallen from low levels from several trees, so had no illusion that he could climb that high in the tree, and if he chances it anyway he's better at climbing so he's less likely to fall.

More off-playground injuries when the playground becomes "protected"? I'd attribute that to the playground becoming boring, and kids looking elsewhere for ways to climb and jump.

As to the rubber mats, I always figured they were chosen for being durable, "green" (as recycled materials), and more comfortable on bare or sandaled feet than woodchips.

My informal anecdotal observances, totally open to confirmation bias, have been that the softer the material the fewer kids you'll find allowed to run barefoot on it. That's also part of the war, do you let your kids run on a playground without shoes, even if it's chilly out. . . . !

I don't know much about the playground specific data, but according to CDC data on unintentional fatal injuries by age, the rates of deaths by suffocation, drowning, and falls for children aged 0 to 14 have fallen dramatically since the 1980s.

Do they break it down? I bet that's pools, largely. I do think improvements in pool safety were overdue, mostly the improvement of having an adult actually watching while the kids are swimming.

So, if you control for risky activity level, kids are better off. I don't believe kids weigh the risks of anything.

They at least think about the potential for immediate pain. So the best safety measure might be something that protects against serious injury but hurts like hell when you fall on it. Maybe deliver mild shocks?

I saw a show on PBS -- I think it was the architecture series with Robert Hughes -- and it showed a couple of fountains at plazas in New York City. One had smoothly curving surfaces and a very high rate of injuries to kids playing in it. The other was composed of large stone cubes, with edges and corners everywhere, and as I recall they had never had an injury. It looked dangerous. That's the way you make a place safe for kids.

If you're climbing, especially someplace with water, don't you need edges to hang on to?

The fountains weren't very high. You might use the cubes as stepping stones, but you wouldn't really be climbing them.

Peltzman did his study before any state passed laws requiring people to use seat belts New York in 1984.

Over that time seat belt usage has grown from under 10% to about 80%.

According to Peltzman this massive jump in seat belt usage should have lead to a major increase in traffic accidents.

But over that time the number of accidents per 100 million vehicle miles fell from 12 to 4, just the opposite of what Peltzman predicted.

So where are all the accident the Peltzman effect called for?

According to Peltzman this massive jump in seat belt usage should have lead to a major increase in traffic accidents.

My understanding of the Peltzman effect is that we should expect little change rather than an increase, because there is usually a trade-off between lower risks and other goals, like saving time or excitement. Depending on how accurately people assess the actual risks, and to what degree lower risks can be traded for other goals, there might be an increase, decrease, or no change in behaviour. The lesson, then, is just that we shouldn't naively expect that enforcing rules, whether abou seatbelts or rubber floors, will reduce the frequency of accidents, especially if people systematically misjudge the risks of different activities or there are clearly other goals which people will trade-off against.

But over that time the number of accidents per 100 million vehicle miles fell from 12 to 4, just the opposite of what Peltzman predicted.

This statistic isn't relevant. It's preposterous to suppose such a prediction could be derived from the logic of the Peltzman effect, if only because there were a million and one confounding developments that occurred during the same period.

Milton Friedman said that you judge an economic theory by how successful its prediction are.

On that basis Peltzman failed miserably.

I don't know whether you're a troll, stupid, or perhaps blinkered by passion, because this response is literally ridiculous.

Of course, successful predictions are important when assessing competing explanations of economic phenomena, but (1) the Peltzman effect isn't an explanation of any particular event, but rather a theoretical framework for constructing such explanations, and (2) nobody ever proposed any such explanation from which you could derive the prediction you mention, so the falsification of that prediction wouldn't count against the explanation, never mind the Peltzman effect.

"The reduction of predicted benefit from regulations that intend to increase safety is sometimes referred to as the Peltzman effect."

And then you state: "Over that time seat belt usage has grown from under 10% to about 80%." (an 8x increase)
"But over that time the number of accidents per 100 million vehicle miles fell from 12 to 4" (a 3x decrease)

"just the opposite of what Peltzman predicted."
No, that's pretty much exactly what the Peltzman effect predicts.

You are confusing the unconditional probability of an accident and the conditional probability of injury given an accident. Seat belts and rubber mats are intended to reduce the latter, and (absent a Peltzman effect, to leave the first unchanged). We would therefore expect a reduction in the unconditional probability of injury, P(Injury) = P(Injury | Accident) * P(Accident)
The risk we are being asked to think about here is P(Injury). If it is to stay roughly constant for auto travel, then P(Accident) must increase, as there is ample evidence that seat belts do in fact reduce severity of injuries.
Back to the OP, is it in fact the case that impacting the play surface is the principal risk for long-bone injuries on the playground? Seems to me falling clear of the jungle gym was way better than getting your leg caught in it on the way down...

parenthesis should close after 'Peltzman effect' ...

Various possibilities.

Demographics, younger drivers are more accident prone and the population has aged.

Increased enforcement of traffic safety regulation such driving while intoxication.

Improvement of roadways, reducing hazardous conditions that were perceived as less hazardous than they actually were.

perhaps people don't have much faith in seatbelts

Milton Friedman said that you judge an economic theory by how successful its prediction are.

On that basis Peltzman failed miserably.

If you do a chart of seat belt usage and the accident rate it looks like an X.

Their correlation is -0.96

But there are plenty of other reasons not to get into a car accident: damage to the car, major and minor injuries that the belt doesn't protect against, legal consequences...all of these are disincentives that aren't tied to seatbelt use.

I don't think the Peltzman effect is terribly valid for seatbelts.

There used to be a lot of macho knuckleheadedness around about how seat belts are dangerous because you want to be "thrown clear" of an accident. How do you get thrown clear? Nobody could explain how it was plausible, just that they heard about this guy who would have been killed if he had been wearing a seat belt, but, fortunately, he got thrown clear.

The Peltzman Effect (new to me) applies only to the parents.

For the kids, the explanation I have heard (and that resonates) is that play is (duh) practice. If you practice physical activity on grounds that control for injury and pain, you don't get the feedback you need to learn properly. It messes up their learning how to assess risk and benefit.

You could, pardon the comparison, probably say the same about some of the school shootings by kids trained up on games with no down side.

As for the insanity of the nanny state and kids' play, it's out of this world and it's very contorted. We fail to protect our kids from the monstrous, but spend huge amounts of time and money "protecting" them from living real lives.

I've had to purposefully change my peer group and my expectations, because after my first kid was a toddler I realized how stunting middle class suburban parenting expectations have become. It's not about broken legs, its about raising kids to be totally afraid of ever having an independent thought. You climb a tree, you have to figure it out, or get together with a kid who knows where to put your feet, which limbs are strong, etc. The playgrounds with watchers, you try to climb *up* a slide or on the *outside* of the steps, a dozen moms with cell phones will be Googling the number for CPS.

well what happens when an adult does the grown equivalent of "try to climb *up* a slide or on the *outside* of the steps"? as parents we help prepare our kids for the world they live in. I am not saying that I am a fan of the hovering just saying it seems to be a feature of modern, risk-averse life.

I was actually just thinking about this -- it's not just our children that we try to protect from risk, sometimes at costs that are too high. And, yes, I think our modeling is sure to be a bigger factor than our recycled rubber chips.

"I’ve had to purposefully change my peer group and my expectations, because after my first kid was a toddler I realized how stunting middle class suburban parenting expectations have become. "

I'm having that debate with my wife now with regards to our young twins. She says they shouldn't get near the creek, because they might fall in, I say yes, that's the point.

I'll take advantage of the age of this thread to ramble, since no one is probably checking back any more!

This was so, so funny. I have an enormous amount of sympathy for your wife. I'm working hard on changing my attitude, as so many women I know are, but it's sure a long and hard road.

I bet you twenty bucks it's not the safety issue. You can mitigate anxiety about safety by hovering, etc. It's the ick factor, isn't it? We've got a river near here, it took me three years to let my kids fully play in it. There were cow pastures up stream! And it was a recreation area without bathrooms -- you know what the implications of that are!!? And, well, of course, you know, brain eating amoebas.

A few thoughts on one of my favorite subjects:
1. It is desperately hard to let your kids take chances if the moms around you won't. Letting your kid play in the cow poop creek while surrounded by moms who continually bathe their kids in Purell is very uncomfortable, socially.
2. For every potential risk there's a little voice saying, "Why take the chance", and there is actually an answer to that sometimes. There's often an excellent reason to take the chance. But when we never take a chance, we don't see the rewards. When you see your child becoming well adjusted, confident, independent, and owning their own risks and safety, you realize you've done good by letting them play in the creek. it makes it easier to take a chance in the next instance. Baby steps is o.k., it can be the way to get there.
3. Water is scary, I'm totally on alert and have a lot of rules and helicopter when my kids are in it. But I've seen one accident with water in the kids' groups I've been in, the kid was o.k., but she was a toddler that mom found floating face down away from the bank in a pond. Thing was, this was at a "safe" playground. Not in any way blaming the mom, accidents happen, but she was talking to friends and there was this feeling that the toddler was on a playground and so pretty much safe, and wariness was down, and the kid wandered off. When I go with groups to the river, we all watch our kids like hawks and peers watch each other because we don't think the city has safety-fied it for us.
4. My kids get fewer common illnesses and they last for less time when we are outside for hours each day. Yes, cow poop in the water is an E. Coli hazard, but we forget the hazard of having kids inside all the time, surrounded by Purell and Clorox fumes. Now that I am getting over my ick factor fear, I recognize that playing in a backyard creek is so much less dangerous in terms of microbes than hanging out in a preschool classroom for the day.

I agree with the Marian Kechlibar post below (if you take the diabetes out, picky me!). Our pediatrician is a self-proclaimed "specialist" in child obesity (ick). Every time we come, we have strained conversations about bike helmets (on our dirt driveway) and sun block. How exactly she expects kids to get out and get "active" when they aren't allowed to move outside without being covered and slime and Kevlar is beyond me. No wonder all her patients prefer video games, no one makes them wear knee pads for that.

The benefits of the behaviors we see as risky are not recognized, and the dangers of activities we see as safe are not recognized. That helps me in trying to adapt. It's very difficult to distinguish between following your instincts and obeying your anxieties. You have to both trust your gut and stiffen your spine. The more you practice, though, the better you get at it.

Although the article never mentions the rise in ADHD diagnoses or the general failure of boys in our educational institutions, these facts seem to be related.

If you're looking for an explanation for why American kids are less creative, less nonconformist, less imaginative, less humourous, and so on, as reported in the article from research by Kyung-Hee Kim, then one obvious explanation is that many children have literally been diagnosed, rather spuriously, with ADHD and prescribed drugs to make them boring, conforming, and easier to manage.

Furthermore, it seems clear that boys revel in and benefit most from the kind of adventure play that the author describes, and so the systemic suppression of such play would seem, on the group level, to hurt boys more than girls. For many kids, and especially boys, the only thing worse than being in trouble with parents and teachers is being bored, and they're chronically bored because they're prevented from engaging in the independent and risky adventure they crave, (though they can emulate this experience, to some extent, by playing videogames about risky adventures). Accordingly, then, they become very disobedient or violent with peers, parents, and teachers, because at least it's something they can do which isn't boring.

Steven Landsburg, in Armchair Economist, using Peltzman in the chapter entitled "seatbelts kill" posits, in jest, that the way to reduce fender benders is to have a large spike from the steering wheel pointed right at the driver's chest!

Its unclear which effect is larger: increased safety from seatbelts, or greater risk taking because of them, but both forces certainly are at work.

E onomists have understood this for a long time. It's always amazing when the public finds it eye opening.

When I was young, 50 years ago, there was no practical way of protecting your children from all sorts of hazard. If your child was injured or worse, killed, your life was massively harmed, but there was one fundamental difference.

Now, if your child is hurt or killed, you will know that you *chose* not to prevent it. We have fewer children, more resources, and far more knowledge about the harms that can befall a child. Instead, you deliberately put your child in harm's way. In fact, there's a good chance after many accidents that you will be charged by the police for failing to take insufficient precautions.

If my mother-in-law is any guide, the risk of having your life utterly destroyed by guilt is *so* great that it's almost unthinkable for any sane parent to let your child take risks that can now be avoided. Needless to say, I'm not entirely sane :-).

(To be fair to my M-I-L, my children actually had to be pushed a little to take the "risks" they needed to establish confidence. Far worse to pro-actively endanger your children by forcing them to take public transit (at 12!) to middle school rather than accept the drive to school their grandmother is willing to give them. (We compromised - she drove them back, which also allowed her to hear how their day went.)

But I was constantly reminded I was *choosing* to put them at risk whenever I allowed (or pushed) them to indulge in anything mildly risky.

No wonder many parents succumb to the pressure to over-protect their children.

I recommend you give your children Handbook of Rigging. It describes how to do incredibly dangerous stuff safely, mostly with regard to the construction of tall buildings. Great book! I recommend the third edition, not so much the later ones unless you need it professionally.

Even if they don't climb the outsides of the tall buildings on their college campus, this book will give them perspective on how to evaluate dangerous procedures and mitigate possible risks.

50 years ago accidents were not the leading cause of death for children and 100 years ago it was only a few %. As fewer children died for other reasons it is only natural that the today´s parents worry more about accidents than parents did in previous generation

When I was a kid, the two dreaded killers were a) plastic bags and b) blasting caps. There were posters in schools showing what blasting caps look like so you can avoid them. You never hear about these dangers anymore.

Yes, this is really a special case of the "first world problem" set.

Much of the this criticism of regulation based on the Peltzman effect overlooks an important point. There is, or may be benefit to the riskier behavior.

Take seat belts. Suppose drivers with seat belts drive faster, because they feel safer. Hence accidents increase, but the extent of injuries and deaths also needs to be considered. And even if that is constant, there is still a gain in that people get places faster. If you want to assess the overall effects, you have to count this sort of benefit as well.

It seems to me that this sort of calculation applies to some other type of safety rules as well, even if you establish that the accident rate is not reduced.

The best theory for that is “risk compensation”—kids don’t worry as much about falling on rubber, so they’re not as careful, and end up hurting themselves more often.

I thought it was dubious to assert the "risk compensation" mechanism for seatbelts. But when it comes to children on a freakin playground it's just laughable. They're not thinking about the relative safety of the different surfaces, and they're especially not acting riskier because of it.

It *might* be worthwhile to check if *parents* are less vigilant about their kids when they believe the surfaces have gotten safer.

Semi-relevant comedy clip:

To me, your comment seems laughable. Of course they will jump from higher up if it does not hurt them.

My seven year old came out the other day, staring at her blisters. We told her she'd have to stop swinging on the bars if she wanted them to heal. Two minutes later, she was back on them, and ten minutes later out celebrating that the bar had worn away one of the skin flaps.

I know a bunch of boys and not a few girls that figure if you're doing something and you don't get hurt, it was hardly worth doing. Getting hurt on the playground is, in MR talk, a feature, not a bug.

Now, getting seriously injured is different, but that takes some connection with consequences, which only develops as you grow up. It doesn't come installed.

Here's a McArdle about letting your kids fall down earlier rather than later, also a bit relevant.

That was a good article. Thanks for posting it.

I'm pretty sure Kids respond to something called the "It Looks Yucky Effect." If you make something look yucky to kids, they'll avoid it. This works much better than making something look hazardous. Kids are too resilient for that. Of course, as we age, we develop a more positive view of yucky. If my kid comes home with a report card of failing grades, I'll tell the school that Megan McArdle told me not to worry about it, just let the kid go ahead and fail, and he'll wind up being Alfred Tarski. Come to think about it, I think the letting my kid fail only works if he is Alfred Tarski.

"If my kid comes home with a report card of failing grades, I’ll tell the school that Megan McArdle told me not to worry about it, just let the kid go ahead and fail, "

Megan McArdle's post was about a 15 year old girl who was afraid to take a class because she might get a B instead of an A and therefore ruin her 4.0 average. Nowhere in the article was there some kind of implicit message that you should be blasé about your kid having "a report card of failing grades".

This might apply only to me, but I'm not sure how people would react if I asked them, "Have you heard of the Peltzman Effect?"

I responded by looking at Wikipedia.
Forget 15 minutes of fame, everyone needs to have at least one effect named after him.

I am not even sure whether the Peltzman effect exists at all with regard to driving seat belt laws. There were too many changes in the car structure in between.

One very important thing is that modern cars isolate you from feelings of speed. I was quite surprised when I drove a 30-y.o. car. It transmitted all the bumps of the road directly to my "behind" and at a higher speed (above 100 kph) the whole structure started to groan as if overloaded. All kinds of various weird sounds filled the car.

This just does not happen in a new car. Therefore, important feedback about the real speed is missing from the driver's environment.

As a result, the driver has a very false perception of the overall safety of the current speed.

For another study that suggests that improving playground safety does have an effect, see below the link below:

This piece seems like another attempt to find a nail for the hammer of the "Peltzman effect". For this actually to work well, children have to have some degree of understanding of how soft the playground surfaces are and the actual risks. This might work if the playgrounds were built on concrete; but this never was the case.

The citation toward of a professor Ball (a good name to have when talking about playgrounds) does not specify how he has measured the changes and lack of changes; thus we can't assess the validity. Greater usage of playgrounds or more playgrounds would increase the frequency of injuries, all else being equal.

BTW: I do agree that many things done in the name of "child safety" are ineffective, overreactions--particularly the great increase in school security measures aimed at stopping outside intruders....

However, those that glorify the "good old days" of greater risk taking, should keep in mind the problem of survivor bias; the posters and writers tend to exclude people who suffered the really bad outcomes we strive to avoid.

I do not think that there ever was time period when deadly injuries from child's play were common.

Perhaps children playing with the grenades on the remains Western front in 1919, but in normal conditions, it is quite uncommon to kill yourself while playing.

On the other hand, the oversheltered generation will have very real and lifelong consequences for their lack of physical movements, such as obesity, diabetes and low fitness levels.

MK, makes an excellent point. What's more risky in the long run? Childhood play injuries or low fitness levels? Granted, those aren't necessarily inverses of each other, but in all likelihood, they are probably highly inversely correlated.

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