In the “Letters” section of today’s New York Times Sunday magazine, a letter by two doctors at the Children’s Hospital of Philadelphia criticizes our piece on car seats vs seat belts:
As pediatricians, scientists and leaders of the world’s largest study on children in crashes, we think that overinterpretation of findings from a single source of data led Stephen J. Dubner and Steven D. Levitt (July 10) to claim that child safety seats are no more effective than seat belts for 2- to 6-year-olds. They examined children in fatal crashes (about 1,200 per year) while ignoring the equally informative data on those in nonfatal crashes (450,000 per year). Our research, which includes over 25,000 in-depth interviews and over 800 crash investigations, consistently shows that child safety seats and booster seats significantly lower the risk of serious injury compared to seat belts alone. Their conclusions stand in stark contrast to the existing body of scientific data that support current child restraint recommendations, and are, in our opinion, irresponsible and dangerous.
Learn the facts at www.chop.edu/carseat. We hope that this misleading article does not cost a child his life.
Dennis Durbin, M.D., and Flaura Winston, M.D.
The Children’s Hospital of Philadelphia
Philadelphia
I may be wrong about car seats, but definitely not for the reason they claim (i.e. that we only look at fatal crashes). I have looked at three other data sets (one with all reported crashes in New Jersey, another with all reported crashes in Wisconsin, and one that is a nationally representative sample of all crashes in the United States). All three of these data sets cover a full set of accidents, not just crashes with fatalities. And in all three data sets the results obtained are virtually identical to the results using the fatal crashes.
Moreover, even in the original paper which did focus on fatal crashes, I employ the techniques of Levitt and Porter (2001) which deal with sample selection (the primary concern one would have with using just fatal crashes) in an extremely convincing manner.
What I find particularly interesting is, despite the NY Times claim that they “fact check” letters to the Sunday magazine, and despite the fact that the NY Times was fully aware that I have analyzed these three additional data sets, they chose to run the letter with this false critique.
I’m not against the Children’s Hospital of Philadelphia folks getting the chance to respond, because I think they deserve that chance, but I find it disturbing that the NY Times would knowingly publish a letter with arguments it knows to be false. Further, I find it interesting that in their “response” on their web site, there is no mention whatsoever of any particular flaws in my analysis, or the issue of my focusing on fatal crashes alone. They simply rehash the prior studies that have been done and say our NY Times column might have “confused” parents.
The prior research, it should be noted, is heavily (though not exclusively) based on a sample that these same doctors have assembled from customers of State Farm Insurance, who the researchers call and ask questions a few days after the accident. While this has been a huge and admirable endeavor on their part, the methodology is not without limitations:
1) A substantial fraction of the State Farm clients decline to respond to the researcher inquiries. No information is provided about how these non-respondents differ from respondents.
2) One could imagine that there are incentives for the respondents to lie about the type of restraint they had their child in. What would you say if you had been driving with your child unrestrained, the child had been injured, and your insurance company called you on the phone a few days later to inquire about details of the crash? If there was no car seat in the vehicle, it would be hard to lie and say you had the child in a car seat since there are police reports. But, you may think that you can get away with saying your child was wearing a seat belt, since all cars have seat belts.
3) If you asked social scientists whether they’d rather have extensive data collected at the crash scene for some universe of crashes, or rely on parent surveys a few days later for your data, I believe that their answer would almost unanimously be that they prefer the universe of crash scene data. Which is precisely the data I am relying on.
About 10 days ago I emailed the director of the team at Children’s Hospital of Philadelphia who do this research, telling her that I would share all my data and programs with them if they were interested, and requesting that they provide the same courtesty to me. She has not responded.
If indeed, the folks at Children’s Hospital of Philadelphia are truly interested in child safety, rather than just being seen as the leaders in child safety, I would hope that they would be willing to work together to figure out why these two sets of results differ so dramatically.
and 
. You can also watch it on 
People like to believe that they can protect their children more than is actually possible. To take away the magical amulet of the car seat is to rob people not only of preconceived notions, but false security. Truth? Schmuth.
(Oh, and don’t forget the car seat manufacturers. They don’t want this data out either.)
It is possible that the doctors simply don’t want to entertain the idea that they might be wrong. This is not an uncommon phenomenon, in my experience; I work in the medical field, and there’s no shortage of ego for many practitioners.
I’ll be watching to see what their response is. It’s sad that they responded in such an ignorant, knee-jerk fashion.
I am in the medical field as well. Unfortunately, I agree with you. I try to be a counter-example.
Shouldn’t that be “Which are precisely the data I am relying on.” ?
But the reason for the NY Times’ behavior seems entirely different to me: fear. We have now been using car seats for many years in America, and have (I think) come to assume they are the safest option for children. Who wants to be the first to use their children to test that theory? Moreover, what major media outlet would want to expose itself to the liability lawsuit from the parent that puts her child in a car seat and has something bad happen?
adeu,
Mateu
Mateu: “data” can take both singular and plural verbs–and the former when it is taken as a mass noun term, like “water” (after all, usually “little data/water”, rather than “few data”). “Data” in the sense of “information” is a mass noun.
I’m disappointed that the NYT didn’t bother to publish the reply–even with a suitable “this letter does not represent our views” disclaimer.
“About 10 days ago I emailed the director of the team at Children’s Hospital of Philadelphia…. She has not responded.”
How do you know that your email got through to her, and was not swallowed by a spam filter?
Steve: I employ the techniques of Levitt and Porter (2001) which deal with sample selection (the primary concern one would have with using just fatal crashes) in an extremely convincing manner.
Yikes. Your analysis is convincing to you. Whoopee.
You and Steve have half a dozen children between you. You have suffered the loss of an infant. Yet you are petulantly pushing your own view here when you think there’s no difference between car seats and seat belts and Children’s Hospital thinks car seats are better.
If you are right but parents believe them, people who buy car seats for toddlers are wasting money. If they are right but parents believe you, children will die.
There is an “asymmetrical loss function.” A person who believes you if you are wrong is in deeper trouble than a person who believes them if they are wrong.
You appear to lack a basic understanding of economics 101.
To anonymous who says I don’t understand econ 101:
You totally miss the point. The goal is to figure out whether car seats work or not. There is an asymmetric loss function only because there is uncertainty about the true parameters. If we knew the true effect of car seats, then we could act accordingly. The point of my research is to learn these parameters.
If car seats don’t work, the answer probably wouldn’t be to throw them away and go merrily on our way. More likely, it would be to take the resources spent on car seats and invest them in something that provides much larger benefits.
There are many things I lack a basic understanding of. I guarantee you that econ 101 is not one of them.
Steve Levitt