Q19 - The use of automobile safety

[bbirdwell]

Two things I noticed first about this argument: it's a causal argument (the increase in car seats is preventing fatalities), and the evidence is percentage-based (serious accidents went up 20%, while child fatalities rose just 10%).

Before looking at the choices, I tried to identify possible logical gaps or assumptions in the argument. One big question that came to mind was "How many accidents include children?" Again, the point the author is making is that, since accidents increased by 20% but child fatalities increased by only 10%, the car seats are preventing fatalities, because presumably, a 20% increase in accidents should yield a 20% increase in child fatalities. But in order for that to be logical, it must be true that all the new accidents (the 20% increase) included the same amount of accidents involving children as accidents usually do.

In other words, if none of the accidents in that 20% increase involved children, then the car seat isn't necessarily helping -- rather, there just aren't as many kid in accidents. So if the car seat is indeed responsible, we must assume that there are still just as many kids involved in accidents as there used to be.

Answer choice (B) essentially validates this assumption. It says "The proportion of kids/accidents has not changed." This means that the 10% increase in child deaths is indeed less than the corresponding 20% we might have expected, thus strengthening the idea that the car seats are preventing deaths.

(A) kids over 5? Who cares. The argument is about those under 4.
(C) kids are taking more, shorter trips? It's unclear how this affects the argument, which relies on accidents and deaths. Number of trips is unrelated.
(D) out of scope. The argument doesn't break the "under 4" category into smaller categories.
(E) number of adult fatalities is out of scope and unrelated.

Hope that helps!

[goriano]

the evidence is percentage-based (serious accidents went up 20%, while child fatalities rose just 10%).

I was a little thrown off by the quoted sentence. I thought that the evidence given is numbers-based. That is, even though the numbers themselves increase by a certain percentage, it is still the numbers that are increasing NOT the likelihood of accidents occurring that is increasing. I'd love to hear a further explanation on this concept. Thanks!

[Alvanith]

the evidence is percentage-based (serious accidents went up 20%, while child fatalities rose just 10%).

I was a little thrown off by the quoted sentence. I thought that the evidence given is numbers-based. That is, even though the numbers themselves increase by a certain percentage, it is still the numbers that are increasing NOT the likelihood of accidents occurring that is increasing. I'd love to hear a further explanation on this concept. Thanks!

I know I might reply too late, but I still would like to say something...

Suppose 8 years ago the total accident number was n, and the rate for kids involved in an accident was x%, and the fatality rate of kids involved in car accidents was y%.

Now we are told the total accident number is 120%n, and the argument assumed the fatality rate should have been near 120%y if there was no increased use of automobile safety seats for kids.

How could this happen if the rate for kids involved in an accident is significantly less than x%, like 0%? To guarantee the assumption of the argument that the fatality rate should have been near 120%y, we have to have a comparable rate for kids involved in an accident. That is, x%, like answer (B).

[Mab6q]

I understand how C is the correct answer, but is there anyway someone could provide a numerical example to make it more clear? Thanks.

[ohthatpatrick]

The correct answer is (B), not (C). Is that what you meant?

If so, here are some pretend numbers:

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Now:
1200 serious auto accidents (20% increase)
? of them involved children
220 of those involved children getting killed

Naturally, I made up all the starting numbers. But from those and using the information given in the stimulus, we know the number of serious accidents and the number of accidents in which kids were killed.

We do NOT know the number/proportion of accidents nowadays that involve children.

What if nowadays, we have:
1200 serious auto accidents (20% increase)
500 of them involved children
220 of those involved children getting killed (10% increase)

compared to 8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Comparing those stats, it looks like we're doing WORSE nowadays than we were 8 years ago.

In each period we had 500 accidents involving kids; nowadays MORE of those accidents involve child fatalities.

Meanwhile, according to (B) you'd have

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

and now
1200 serious auto accidents (20% increase)
600 of them involved children (20% increase)
220 of those involved children getting killed (10% increase)

This shows improvement. 220/600 is a lower fatality rate than 200/500.

Hope this helps.

[Mab6q]

The correct answer is (B), not (C). Is that what you meant?

If so, here are some pretend numbers:

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Now:
1200 serious auto accidents (20% increase)
? of them involved children
220 of those involved children getting killed

Naturally, I made up all the starting numbers. But from those and using the information given in the stimulus, we know the number of serious accidents and the number of accidents in which kids were killed.

We do NOT know the number/proportion of accidents nowadays that involve children.

What if nowadays, we have:
1200 serious auto accidents (20% increase)
500 of them involved children
220 of those involved children getting killed (10% increase)

compared to 8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Comparing those stats, it looks like we're doing WORSE nowadays than we were 8 years ago.

In each period we had 500 accidents involving kids; nowadays MORE of those accidents involve child fatalities.

Meanwhile, according to (B) you'd have

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

and now
1200 serious auto accidents (20% increase)
600 of them involved children (20% increase)
220 of those involved children getting killed (10% increase)

This shows improvement. 220/600 is a lower fatality rate than 200/500.

Hope this helps.

Yes I meant B . Thanks for the great example!

[shen8115]

The correct answer is (B), not (C). Is that what you meant?

If so, here are some pretend numbers:

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Now:
1200 serious auto accidents (20% increase)
? of them involved children
220 of those involved children getting killed

Naturally, I made up all the starting numbers. But from those and using the information given in the stimulus, we know the number of serious accidents and the number of accidents in which kids were killed.

We do NOT know the number/proportion of accidents nowadays that involve children.

What if nowadays, we have:
1200 serious auto accidents (20% increase)
500 of them involved children
220 of those involved children getting killed (10% increase)

compared to 8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

Comparing those stats, it looks like we're doing WORSE nowadays than we were 8 years ago.

In each period we had 500 accidents involving kids; nowadays MORE of those accidents involve child fatalities.

Meanwhile, according to (B) you'd have

8 yrs ago:
1000 serious auto accidents
500 of them involved children
200 of those involved children getting killed

and now
1200 serious auto accidents (20% increase)
600 of them involved children (20% increase)
220 of those involved children getting killed (10% increase)

This shows improvement. 220/600 is a lower fatality rate than 200/500.

Hope this helps.

Yes I meant B . Thanks for the great example!

How did you get the number 600 (20% increase) if the proportion of accidents involving child passengers remained constant?

[livia.maas]

"How did you get the number 600 (20% increase) if the proportion of accidents involving child passengers remained constant?"

600/1200 = 50%, just like 500/1000 = 50%. Therefore, the proportion of serious accidents involving child passengers (serious accidents involving child passengers/total serious accidents) remained constant at 50%.

Hope that helps!

[LsatCrusher822]

Can somebody please explain why C isnt correct? I thought maybe if the number of trips went up, that would remove an alternative explanation for the reduction in fatalities (i.e., if the trips were indeed lower, then that may be the reason why child fatalities are lower). Same goes for the time spent in a car. Wouldnt being in a car longer expose you to higher possibility of fatalities? So if the time spent is the same, wouldnt that also remove a potential weakness with this argument?

[LauraS737]

(C) kids are taking more, shorter trips? It's unclear how this affects the argument, which relies on accidents and deaths. Number of trips is unrelated.

I get why (B) is correct, but could you explain why (C) is incorrect in more detail?

My though process was because there are more trips involved with children, even if average time spent in cars remains unchanged, there is a greater risk for them to be in accidents and die. However, because the safety seats are preventing those accidents, even though a greater risk for accidents is posed, the safety seats are saving the children, which would strengthen the arg?

Where am I going wrong?

[YajingW401]

The number of children killed
= total number of accidents × the proportion of accidents involving child passengers × the death rate of children in accidents

Let's do some math.

As the number of children killed increased less than the total number of accidents did, then the product of the proportion of accidents involving child passengers and the death rate is going down.

Then an unchanging proportion of accidents involving child passengers would be great support for determing the death rate is going down as well.

So easy. Other choice would not affect any parameter in the formula above.