PrepTest 149, Section 1, Question 5
Researchers examined 100 people suffering from herniated disks(49 more words not shown)
Which one of the following,(7 more words not shown)
- AThe researchers also(23 more words not shown)
- BWhen the researchers(22 more words not shown)
- CWhen the researchers(31 more words not shown)
- DAnother team of(24 more words not shown)
- EWhen the researchers(35 more words not shown)
Reading the argument
Five people out of a hundred have the gene defect. Is that unusual? If roughly 5 percent of people generally had it, finding five in a group with back problems might not tell us much by itself.
The comparison group makes it more interesting: none of the hundred people with healthy disks had the defect. That suggests a possible connection, but could this small difference be a coincidence? Imagine finding five blond people in one group and none in the other. We wouldn't immediately conclude that blond hair increases the risk of a herniated disk.
What we’re looking for
To strengthen the researchers' reasoning, I'd want more reason to think the pattern is meaningful. For example, if the defect were extremely rare, finding several cases together in the affected group could be more striking. That's one possible route. The broader goal is evidence tying the defect to increased risk, without requiring it to explain every herniated disk.
Working the answers
- A
This gives a high rate of herniated disks among people without the defect. By itself, it doesn't show that people with the defect have an even higher risk. Noncarriers are a relevant comparison group, but we would need the right comparison to use their rate in support of the claim. Showing that many noncarriers have back problems doesn't establish the increased risk attributed to the gene.
- B
Two out of a hundred is 2 percent. Is that high or low compared with people without the defect? We aren't told. A 2 percent rate could support increased risk if the comparable rate without the defect were far lower, but it wouldn't if that other rate were higher. We can't decide that this strengthens merely from the carrier group's number alone.
- CCorrect
We now have thirty additional relatives with the defect, and every one of those relatives has herniated disks. That extends the connection well beyond the original five cases and gives us more reason to investigate the defect as a contributor to the problem.
It doesn't prove that the gene caused their condition. Family members might share a lifestyle or some other relevant factor. And it doesn't say that everyone in the world with the defect has herniated disks. Still, finding the condition in all thirty of these additional carriers supports the proposed link. A strengthener can help without settling every alternative explanation.
- D
People can have herniated disks without this defect even if the defect increases the risk. We already knew most people in the original affected group lacked it. Another affected group without the gene doesn't add support for the gene's effect, but it also doesn't establish that the gene can have no effect. Increased risk is different from being a required cause.
- E
These relatives don't have the defect, and many still have herniated disks. Like A, this shows that the condition can occur without the gene. It doesn't tell us whether carrying the gene raises the likelihood. C is more helpful because it adds cases in which the defect and the condition occur together.
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