PrepTest 155, Section 1, Question 10
Dentist: Five recently conducted studies all show that(45 more words not shown)
Which one of the following,(8 more words not shown)
- AToothpaste containing fluoride(10 more words not shown)
- BNearly all dentists(16 more words not shown)
- CDental hygiene is(12 more words not shown)
- DOn average, children(13 more words not shown)
- EThe diets of(17 more words not shown)
Reading the argument
What if the fluoride helps, but something else is worse for American children's teeth?
The studies compare children in places with fluoridated water against children in places without it. A higher proportion of children in the fluoridated-water group have decayed, missing, or filled teeth. That doesn't isolate what the water is doing. Perhaps American children eat more sugar. Perhaps European children brush more carefully. Either difference could mask a benefit from fluoridation.
Imagine that sugary diets increase tooth decay while fluoridated water reduces it. American children could still end up with more decay overall because the dietary disadvantage outweighs the benefit. That's a possible explanation of the figures, not a new fact about either population.
What we’re looking for
The dentist concludes that fluoridating water has no substantial tendency to prevent decay. To strengthen that claim, we could rule out competing differences. Tell us the diets aren't worse, or that the children actually care for their teeth similarly. That would make the comparison more informative about the water.
Working the answers
- A
Widely available doesn't mean equally used. Both groups could have access to fluoride toothpaste while using it at different rates. And the dentist's conclusion concerns fluoride in water, not merely the existence of another product containing fluoride. A doesn't make the groups' actual exposure or habits comparable.
- B
This tells us about direct fluoride treatments by American dentists. It doesn't tell us how that compares with European treatment, how often the children receive it, or what effect fluoridated water itself has. We can't get from a common dental practice to the dentist's conclusion about the water supply.
- C
This is tempting because it addresses an alternative explanation: perhaps American children aren't even taught dental hygiene. C rules out that simple possibility. But being taught the subject doesn't mean the instruction is equally effective or the children follow it equally well. Parents might enforce brushing differently at home. C offers, at most, a small amount of help; it leaves the actual habits unresolved.
- D
More frequent European checkups give us another possible explanation for Europe's better results. Imagine children there receive three checkups a year while American children receive two. Their teeth could be better because of that care, even while fluoride helps the American group. This undermines the comparison as evidence against fluoridating water.
- ECorrect
This directly addresses the dietary objection. We can't explain the American children's worse results by saying their diets are generally worse for their teeth, because E rules that out. It doesn't eliminate every possible difference between the groups or prove the dentist's conclusion. But it removes a concrete alternative explanation more directly than C's statement about what children are taught.
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