As a parent of 2 a big reason we won’t have a third is the massive step up in transportation costs. Having to get a third car seat would require us to go from our Kia to a minivan. And then there is the cost of the car seat alone.
Then there is the time cost of wrangling kids in an out of them. My toddler can easily make it 15 minutes to buckle her in just on her own. A third would mean easily 5 minutes of to get everyone buckled in and only if they are cooperative.
Yep, there is like two brands that specialize in three across.
A lot of new parents haven't yet realized that a carseat is wider than the average adult. Meaning that cramped middle seat isn't getting a third seat without very careful consideration and the right vehicle.
As a father of four (2+2: third one was born after 8 years since the second one), I thought all the trouble in the world would come and go, but what'll stay is us having a second life with kids when older ones get all independent teenagers. And we are not 40 yet.
The transportation costs are annoying, but worth it.
> We show that laws mandating use of child car safety seats significantly reduce birth rates, as many cars cannot fit three child seats in the back seat.
Wouldn't the real cause of the depressed birthrates be the requirement to own a car in order to have children? If you aren't a slave to your vehicle there's no problem with the available space for car seats.
If you aren't a slave to your car, you likely live in a walkable area where the cost of a 4-bedroom apartment or house is going to be pretty high. I'm not saying you can't raise kids in a 2 or 3 bedroom apartment, and when I lived in apartments many families had kids in a 1-bedroom apartment, but it's very tight and many people would consider it a significant hardship for both the kids and the parents.
I would also add as a car slave that the kinds of cars large enough to fit the kinds of car seats marketed in the US are tens of thousands more than a compact or mid-size sedan, and that in a mid-size sedan having a car seat in the rear-facing configuration significantly constrains how far back you can put the passenger or driver seat. This is true even for the narrower seats that are designed for three-across seating. And worse, you might not have the latch system or an appropriate kind of seat belt on that third seat.
> If you aren't a slave to your car, you likely live in a walkable area where the cost of a 4-bedroom apartment or house is going to be pretty high.
Or you're one of the millions of people who live in developing countries which have low cost of living and low housing costs. Coincidentally this group has very high birth rates.
Also, socially conservative, multi-generational households (sharing labour and childcare between women relatives), less expectation for mothers of young kids to be away from the home, and a much lower expectation of what "housing" means in terms of both building quality and the amount of living space per person.
Or you are poor enough you get paid to pop out more kids and it's cheaper to uber twice a month to the grocery store because you have no job for which you'd need a car nor the cash to buy it.
I think the car is a proxy/correlation for a level of wealth. If you make little enough the marginal cost of the next kid "seems" cheap because you basically make it back in state benefits in a lot of cases.
Double-buggies on public transport and more than two kids on a typical cargo cycle aren't fun either. Granted the age-span that's necessary is a little shorter than car seats.
That said, have 3 kids aged within 5 years of one another and we never had to get a double buggy. The older ones would be OK to walk (3 year olds will walk a pretty long way if you're patient) by the time the youngest got too big to be sling-carried.
It comes down to, dealing with three under-5's single-handed while out and about is pretty hectic full stop. Most places with high birth rates "solve" this by not allowing mums the expectation to be away from the house much, and/or they're multigenerational households where grandma or an aunt can be home with some of the kids.
So to your point, I think it's less the requirement to own a car, more the expectation of a kind of lifestyle which often, though not always, in turn requires one. Childcare for 2 year olds here is often upwards of $2500/month, now that's a contraceptive.
I had a Mazda 3 hatchback, fun little car with stick shift, when our second child arrived. It was not possible to fit in a second rear-facing car seat behind driver AND have the driver seat be in any acceptable position for me or my wife, there was just no space left in front. We researched the seats and ultimately it was easier to get a bigger car than mess with it, so we got a Volvo XC70 that had plenty of space. Once the kids could face forward, the typical Graco style seats were too wide and the middle rear passenger seat was not usable, so we invested into 2 narrow-profile seats that left the middle seat more useful. I can't remember the brand anymore, but it took a lot of research to find the narrow ones and they weren't cheap.
And none of this have contributed to us not wanting more than 2 children. That wasn't going to happen regardless of any car seats. People not wanting to have more than a 1 or 2 kids has so many other, more important reasons, I very much doubt that car seat size has much to do with it.
I also think that modern car seats are one of the main factors driving the adoption of unnecessarily large cars, which have far worse safety outcomes in crashes for everybody except the people inside them.
When I was growing up in the 90s with 2 siblings we had a small hatch. When I had my second child we had to upgrade from a small hatch to an SUV because we simply couldn't fit a car seat behind the driver. Even now, I'm not sure if a third would fit.
Sure, the SUV itself and the extra padding on the car seats might make my children safe in collisions with other big cars, but if we were all still driving hatches then maybe none of that would be necessary.
(Have 3yo and 1yo, another one the way, goal is 4)
I have often thought that car seats are one of the major drags of modern parenting. This study apparently (I don't have time to read it, too busy with kids lmao!) confirms my suspicions.
It is unfortunate that every policy change around them is trading some amount of convenience for every smaller risk eliminations. It is essentially impossible to say perfectly rational things like "I think children should be put in this slightly riskier type of car seat for convenience reasons."
Even if laws are relaxed, there is the peer/manufacturer pressure. As a real example, I think it is pretty annoying to have my three year old facing backwards. It would be somewhat more dangerous to have them facing forwards, but a substantial improvement in quality of life for me and for the child. The manufacturers compete based on max weight that they support/allow/claim for rear facing, something like 45 pounds. So a family member such as a spouse allegedly has decided that the child ABSOLUTELY needs to be rear facing until they reach that weight. That may not happen until age five! By this time there may be manufacturers inching up to 60 pounds rear facing.
The only possible relief I can envision is that computers become so proficient at driving our cars that there are essentially no accidents. Then we may be allowed to sit unbuckled holding our children!
My child moved to front facing at around 2 or maybe 2.5 at the oldest (had to go back and lock at old pictures to confirm, she’s 12 now). Parents who obsess over things like keeping their kid rear facing until 5 or in a booster seat until 12 are just neurotic, IMHO. They’re probably the same ones who won’t let them ride their bikes around the neighborhood unsupervised or walk/ride the bus to or from school.
I had a vehicle with no back seats when my child was in a car seat. It was great because I could attend to them while driving. Since there were no back seats they could not cite me as it was an exception to the law.
I'm not convinced it's actually safer to have kids in the back. Sure they're safer in an accident, but when I drove another car with rear seats I found myself constantly looking back to deal with the child thus more likely to cause an accident. Yes maybe you should just neglect your child while driving, but they will exact penance if you do so, by non-stop screaming so loud you can't hear emergency vehicles or other possible road hazards.
This common sense mindset would invalidate so many 'safety' laws and I'm all for it.
Studies make so many invalid assumptions (and usually don't even state them) to force the data / statistics to fit clean a/b or null testing.
But to put a dent in the status quo, we really need a greenlight to just dump however many kids in the back again, no matter the number of kids or seatbelts.
And before anyone gut reacts to this- ask yourself why doing that with schoolbuses still isn't a problem?
Probably for the same reason government trucks aren't required to have emissions controls on them, at the end of the day the King will do whatever they like and reason backwards why it applies to the subjects but not the crown.
> I'm not convinced it's actually safer to have kids in the back.
I thought that a major reason for placing children in back seat was because of the air bags in the front seat representing a danger to them when they deploy.
(But maybe kids don't trigger the weight needed to activate the passenger side air bag anymore?)
You can also usually just turn off the passenger-side airbag. I know there's been a button on every car I've owned to do so, for when you've got something heavy in the front seat that isn't a passenger.
It's definitely possible to put 3 car seats across in the back seat of pretty much any car available in the American market. The appropriate narrow seats just aren't very popular or well known...
Let’s just focus on how cars and car culture are reducing birth rates. Nobody wants to chuck their kids into the back seat without a carseat any more. Laws aren’t the problem.
These seem like particularly specific excuses. If you are not into having kids, there are many different ways to rationalize that (but why?). If you are into kids, you'd have to overcome all sorts of pain and suffering, car culture is by far not the worst of them.
I was going to have more kids, but I didn't for the particular exact reasons I always am harping on about (in my case, nerfing beast hunter in WoW in 2018) ;)
I thought this was going to be about a car being uncomfortable to have sex in.
Such a car would make for a great product to sell to parents of teenagers, so you can lend them the car but at least make it difficult to fornicate without consent of the king.
> We estimate that these laws prevented fatalities of 57 children in car crashes in 2017 but reduced total births by 8,000 that year and have decreased the total by 145,000 since 1980.
It's just not cool to have kids. There are many more ways to have fun and status in society, so having kids is either coming as a social burden ("i am expected to by my spouse/relatives"), or a religious thing. Rationally, it's such a pain in the ass to have kids, while you can have some much more fun without them: travel the world, meet people, learn and explore! Clearly, having kids is net cost and suffering.
Yet, those who opt in do have a different opinion. We got two a decade ago, and then a couple years ago through of FOMO that when we are 45 we'd look back and regret missing the window of having another couple of kids. So we did. I'm 39, have four kids, had to get a bigger car, pay the airline tickets through the nose, spend a lot of time on kids' stuff, and love it. My family is the center of the universe and I'm the happiest and wisest dad alive. Everyone else is childish ;-P
The law in my state doesn't require car seats be in the back if it's full or not possible. IIRC they also aren't required if there's no more room. I put my kid up front in my truck that had zero back seats, only a couple people said anything and I told them to pound sand, it certainly wasn't illegal.
Legal or not, there are real safety reasons not to put a small child up front. I bet your car's user manual says not to put kids up front. The safety systems are designed with minimum height & weight assumptions. The front seat belts aren't designed for a car seat. But most importantly, airbags explode with serious force that can break bones in a kids face. If they're in a rear facing car seat it can strike the seat (which will be close to the dashboard) with enough force to snap their spine.
>Legal or not, there are real safety reasons not to put a small child up front. I bet your car's user manual says not to put kids up front. The safety systems are designed with minimum height & weight assumptions. The front seat belts aren't designed for a car seat. But most importantly, airbags explode with serious force that can break bones in a kids face. If they're in a rear facing car seat it can strike the seat (which will be close to the dashboard) with enough force to snap their spine.
He already said he told people who were hand wringing to pound sand. What's the point of more hand wringing?
Also, trucks from the 90s typically even have passenger airbags.
It was never about the limit of the law. It was always about what will get you scolded or otherwise harassed by other parents or people in the "children" profession. Any sort of place lots of kids are (daycare, doctor, etc, etc) are absolute hives of those kinds of people.
> I put my kid up front in my truck that had zero back seats, only a couple people said anything and I told them to pound sand, it certainly wasn't illegal.
Yeah because at that point you're basically advertising that you don't give a shit what they think and so you're a lost cause to the kind of people who'd try and guilt you.
I bet if you showed up wearing both a front and rear kid carrier while riding a motorcycle they would have not said a word and avoided I contact with you entirely.
A theory that at least is consistent with the observed correlation seems vastly superior to a midbrow dismissal that doesn't. Your "raising kids is hard" theory would explain why people don't have a third child, but raising kids is hard universally. What was observed was that a third child was delayed for longer (even indefinitely) in states with higher age thresholds for mandatory car seats (even when controlling for demographics).
Their causal explanation relies on two additional observations that seem pretty hard to explain by other theories: the effect disappears for single-parent and carless households.
It is also the number at which your reproduction exceeds that of only replacing your own life. This is very important to some parents to leave the world with more people in it.
As a parent of 2 a big reason we won’t have a third is the massive step up in transportation costs. Having to get a third car seat would require us to go from our Kia to a minivan. And then there is the cost of the car seat alone.
Then there is the time cost of wrangling kids in an out of them. My toddler can easily make it 15 minutes to buckle her in just on her own. A third would mean easily 5 minutes of to get everyone buckled in and only if they are cooperative.
Yep, there is like two brands that specialize in three across.
A lot of new parents haven't yet realized that a carseat is wider than the average adult. Meaning that cramped middle seat isn't getting a third seat without very careful consideration and the right vehicle.
The one we use is diono but there may be others, and apparently in the UK you can get 4 across - https://www.youtube.com/shorts/AEwtjK-U5X0 or https://www.multimac.com - not rated for the USA, but in the USA if you have 4 kids they just issue you an APC ;)
Daycare is like 3000eur/month for 3+ years. You can probably lease a double decker for that money
As a father of four (2+2: third one was born after 8 years since the second one), I thought all the trouble in the world would come and go, but what'll stay is us having a second life with kids when older ones get all independent teenagers. And we are not 40 yet.
The transportation costs are annoying, but worth it.
> We show that laws mandating use of child car safety seats significantly reduce birth rates, as many cars cannot fit three child seats in the back seat.
Wouldn't the real cause of the depressed birthrates be the requirement to own a car in order to have children? If you aren't a slave to your vehicle there's no problem with the available space for car seats.
If you aren't a slave to your car, you likely live in a walkable area where the cost of a 4-bedroom apartment or house is going to be pretty high. I'm not saying you can't raise kids in a 2 or 3 bedroom apartment, and when I lived in apartments many families had kids in a 1-bedroom apartment, but it's very tight and many people would consider it a significant hardship for both the kids and the parents.
I would also add as a car slave that the kinds of cars large enough to fit the kinds of car seats marketed in the US are tens of thousands more than a compact or mid-size sedan, and that in a mid-size sedan having a car seat in the rear-facing configuration significantly constrains how far back you can put the passenger or driver seat. This is true even for the narrower seats that are designed for three-across seating. And worse, you might not have the latch system or an appropriate kind of seat belt on that third seat.
> If you aren't a slave to your car, you likely live in a walkable area where the cost of a 4-bedroom apartment or house is going to be pretty high.
Or you're one of the millions of people who live in developing countries which have low cost of living and low housing costs. Coincidentally this group has very high birth rates.
Also, socially conservative, multi-generational households (sharing labour and childcare between women relatives), less expectation for mothers of young kids to be away from the home, and a much lower expectation of what "housing" means in terms of both building quality and the amount of living space per person.
Who expects mothers of young kids in the US to be away from the home?
Or you are poor enough you get paid to pop out more kids and it's cheaper to uber twice a month to the grocery store because you have no job for which you'd need a car nor the cash to buy it.
The research is about the falloff in family size from 2 children to 3 children.
> If you aren't a slave to your vehicle there's no problem with the available space for car seats.
The abstract says the effect is limited to households with a car.
I think the car is a proxy/correlation for a level of wealth. If you make little enough the marginal cost of the next kid "seems" cheap because you basically make it back in state benefits in a lot of cases.
Double-buggies on public transport and more than two kids on a typical cargo cycle aren't fun either. Granted the age-span that's necessary is a little shorter than car seats.
That said, have 3 kids aged within 5 years of one another and we never had to get a double buggy. The older ones would be OK to walk (3 year olds will walk a pretty long way if you're patient) by the time the youngest got too big to be sling-carried.
It comes down to, dealing with three under-5's single-handed while out and about is pretty hectic full stop. Most places with high birth rates "solve" this by not allowing mums the expectation to be away from the house much, and/or they're multigenerational households where grandma or an aunt can be home with some of the kids.
So to your point, I think it's less the requirement to own a car, more the expectation of a kind of lifestyle which often, though not always, in turn requires one. Childcare for 2 year olds here is often upwards of $2500/month, now that's a contraceptive.
I had a Mazda 3 hatchback, fun little car with stick shift, when our second child arrived. It was not possible to fit in a second rear-facing car seat behind driver AND have the driver seat be in any acceptable position for me or my wife, there was just no space left in front. We researched the seats and ultimately it was easier to get a bigger car than mess with it, so we got a Volvo XC70 that had plenty of space. Once the kids could face forward, the typical Graco style seats were too wide and the middle rear passenger seat was not usable, so we invested into 2 narrow-profile seats that left the middle seat more useful. I can't remember the brand anymore, but it took a lot of research to find the narrow ones and they weren't cheap.
And none of this have contributed to us not wanting more than 2 children. That wasn't going to happen regardless of any car seats. People not wanting to have more than a 1 or 2 kids has so many other, more important reasons, I very much doubt that car seat size has much to do with it.
I also think that modern car seats are one of the main factors driving the adoption of unnecessarily large cars, which have far worse safety outcomes in crashes for everybody except the people inside them.
When I was growing up in the 90s with 2 siblings we had a small hatch. When I had my second child we had to upgrade from a small hatch to an SUV because we simply couldn't fit a car seat behind the driver. Even now, I'm not sure if a third would fit.
Sure, the SUV itself and the extra padding on the car seats might make my children safe in collisions with other big cars, but if we were all still driving hatches then maybe none of that would be necessary.
We are in the stupidest arms race.
(Have 3yo and 1yo, another one the way, goal is 4)
I have often thought that car seats are one of the major drags of modern parenting. This study apparently (I don't have time to read it, too busy with kids lmao!) confirms my suspicions.
It is unfortunate that every policy change around them is trading some amount of convenience for every smaller risk eliminations. It is essentially impossible to say perfectly rational things like "I think children should be put in this slightly riskier type of car seat for convenience reasons."
Even if laws are relaxed, there is the peer/manufacturer pressure. As a real example, I think it is pretty annoying to have my three year old facing backwards. It would be somewhat more dangerous to have them facing forwards, but a substantial improvement in quality of life for me and for the child. The manufacturers compete based on max weight that they support/allow/claim for rear facing, something like 45 pounds. So a family member such as a spouse allegedly has decided that the child ABSOLUTELY needs to be rear facing until they reach that weight. That may not happen until age five! By this time there may be manufacturers inching up to 60 pounds rear facing.
The only possible relief I can envision is that computers become so proficient at driving our cars that there are essentially no accidents. Then we may be allowed to sit unbuckled holding our children!
My child moved to front facing at around 2 or maybe 2.5 at the oldest (had to go back and lock at old pictures to confirm, she’s 12 now). Parents who obsess over things like keeping their kid rear facing until 5 or in a booster seat until 12 are just neurotic, IMHO. They’re probably the same ones who won’t let them ride their bikes around the neighborhood unsupervised or walk/ride the bus to or from school.
My wife's argument to keep them rear-facing as long as possible is that it's closer to laying down and it helps them sleep.
I had a vehicle with no back seats when my child was in a car seat. It was great because I could attend to them while driving. Since there were no back seats they could not cite me as it was an exception to the law.
I'm not convinced it's actually safer to have kids in the back. Sure they're safer in an accident, but when I drove another car with rear seats I found myself constantly looking back to deal with the child thus more likely to cause an accident. Yes maybe you should just neglect your child while driving, but they will exact penance if you do so, by non-stop screaming so loud you can't hear emergency vehicles or other possible road hazards.
This common sense mindset would invalidate so many 'safety' laws and I'm all for it.
Studies make so many invalid assumptions (and usually don't even state them) to force the data / statistics to fit clean a/b or null testing.
But to put a dent in the status quo, we really need a greenlight to just dump however many kids in the back again, no matter the number of kids or seatbelts.
And before anyone gut reacts to this- ask yourself why doing that with schoolbuses still isn't a problem?
Probably for the same reason government trucks aren't required to have emissions controls on them, at the end of the day the King will do whatever they like and reason backwards why it applies to the subjects but not the crown.
> I'm not convinced it's actually safer to have kids in the back.
I thought that a major reason for placing children in back seat was because of the air bags in the front seat representing a danger to them when they deploy.
(But maybe kids don't trigger the weight needed to activate the passenger side air bag anymore?)
You can also usually just turn off the passenger-side airbag. I know there's been a button on every car I've owned to do so, for when you've got something heavy in the front seat that isn't a passenger.
It's definitely possible to put 3 car seats across in the back seat of pretty much any car available in the American market. The appropriate narrow seats just aren't very popular or well known...
Even the supposed narrow ones can be a pain in the arse to actually get in the back.
Every family I see with at least 2 kids has a minivan, so maybe we can discuss if minivans are causal.
I didn’t need the minivan until the third kid appeared. I would have stayed with a sedan as long as possible.
We ran the sedan through 3 but really should have moved to the minivan much earlier; they're just much more practical for almost everything.
I didn't come across those narrow seats when we looked into solution for fitting two kids and an adult (grandma) in the back row.
So we went for (especially in Europe) rather limited subset of cars where all 3 of the 2nd row seats are proper sized, with Isofix on each of them.
Usually same makes/models that offer the option of additional 2 seats in the 3rd row.
Only for some North American models. The narrow seats are mandatory to even try but even then some cars are 3-4 inches too narrow door to door.
Let’s just focus on how cars and car culture are reducing birth rates. Nobody wants to chuck their kids into the back seat without a carseat any more. Laws aren’t the problem.
Cars and car culture probably increased birth rates in the last few decades to begin with!
These seem like particularly specific excuses. If you are not into having kids, there are many different ways to rationalize that (but why?). If you are into kids, you'd have to overcome all sorts of pain and suffering, car culture is by far not the worst of them.
(Father of 4, 39 y.o., non-religious.)
I was going to have more kids, but I didn't for the particular exact reasons I always am harping on about (in my case, nerfing beast hunter in WoW in 2018) ;)
back seat? we were loose in the pickup truck!
You had a truck! Lucky! We just rolled around like billiard balls in a station wagon.
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I wonder if self-driving cars and massively improved safety will solve this.
5 kids in a car, held, seated, seatbelted, any-which-way. Like on a train.
No parent will ever do that, because parenting fucks up brain in a special way
I thought this was going to be about a car being uncomfortable to have sex in.
Such a car would make for a great product to sell to parents of teenagers, so you can lend them the car but at least make it difficult to fornicate without consent of the king.
Anyway stow-n-go minivans are the best for ... carrying (and making) lots of kids
Minivans cause minivans?
That was immediately my thought.
A friend once remarked that it'd take particular dedication to so using a Miata.
When did any of that ever stop teenagers?
> We estimate that these laws prevented fatalities of 57 children in car crashes in 2017 but reduced total births by 8,000 that year and have decreased the total by 145,000 since 1980.
145K is roughly the population of Syracuse, NY or Midland, TX. That is far more than the absolute number of US military deaths in World War I (116,516 per https://en.wikipedia.org/wiki/United_States_military_casualt...).
It's just not cool to have kids. There are many more ways to have fun and status in society, so having kids is either coming as a social burden ("i am expected to by my spouse/relatives"), or a religious thing. Rationally, it's such a pain in the ass to have kids, while you can have some much more fun without them: travel the world, meet people, learn and explore! Clearly, having kids is net cost and suffering.
Yet, those who opt in do have a different opinion. We got two a decade ago, and then a couple years ago through of FOMO that when we are 45 we'd look back and regret missing the window of having another couple of kids. So we did. I'm 39, have four kids, had to get a bigger car, pay the airline tickets through the nose, spend a lot of time on kids' stuff, and love it. My family is the center of the universe and I'm the happiest and wisest dad alive. Everyone else is childish ;-P
What I've seen is that when you have no kids, DINKing it up, everyone you know has no kids and having kids seems impossible.
But as they start having kids, you start having kids - and you can roughly keep the same group, maybe get a few, lose a few.
But if you get up to 4 (or more) kids, you start finding ... your group changes to one that includes more and larger families.
I was expecting to read about flame retardants in car seats causing infertility.
The law in my state doesn't require car seats be in the back if it's full or not possible. IIRC they also aren't required if there's no more room. I put my kid up front in my truck that had zero back seats, only a couple people said anything and I told them to pound sand, it certainly wasn't illegal.
Legal or not, there are real safety reasons not to put a small child up front. I bet your car's user manual says not to put kids up front. The safety systems are designed with minimum height & weight assumptions. The front seat belts aren't designed for a car seat. But most importantly, airbags explode with serious force that can break bones in a kids face. If they're in a rear facing car seat it can strike the seat (which will be close to the dashboard) with enough force to snap their spine.
>Legal or not, there are real safety reasons not to put a small child up front. I bet your car's user manual says not to put kids up front. The safety systems are designed with minimum height & weight assumptions. The front seat belts aren't designed for a car seat. But most importantly, airbags explode with serious force that can break bones in a kids face. If they're in a rear facing car seat it can strike the seat (which will be close to the dashboard) with enough force to snap their spine.
He already said he told people who were hand wringing to pound sand. What's the point of more hand wringing?
Also, trucks from the 90s typically even have passenger airbags.
That seems reasonable. Which state do you live in?
AZ
It was never about the limit of the law. It was always about what will get you scolded or otherwise harassed by other parents or people in the "children" profession. Any sort of place lots of kids are (daycare, doctor, etc, etc) are absolute hives of those kinds of people.
> I put my kid up front in my truck that had zero back seats, only a couple people said anything and I told them to pound sand, it certainly wasn't illegal.
Yeah because at that point you're basically advertising that you don't give a shit what they think and so you're a lost cause to the kind of people who'd try and guilt you.
I bet if you showed up wearing both a front and rear kid carrier while riding a motorcycle they would have not said a word and avoided I contact with you entirely.
Correlation does not equal causation. I feel this study shows correlation, but fails to prove any associated causation.
Maybe people just avoid 3 kids, because it’s hard enough raising one or two kids.
A theory that at least is consistent with the observed correlation seems vastly superior to a midbrow dismissal that doesn't. Your "raising kids is hard" theory would explain why people don't have a third child, but raising kids is hard universally. What was observed was that a third child was delayed for longer (even indefinitely) in states with higher age thresholds for mandatory car seats (even when controlling for demographics).
Their causal explanation relies on two additional observations that seem pretty hard to explain by other theories: the effect disappears for single-parent and carless households.
Or cars usually fit 2 child seats because that's the common number they get from customer research.
It is also the number at which your reproduction exceeds that of only replacing your own life. This is very important to some parents to leave the world with more people in it.
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