PrepTest 134, Section 1, Question 13
Medical researcher: Scientists compared a large group of(41 more words not shown)
Which one of the following,(9 more words not shown)
- AFor both groups(23 more words not shown)
- BAmong the joggers(22 more words not shown)
- CMost jogging injuries(20 more words not shown)
- DThe more prone(22 more words not shown)
- EStudies have found(18 more words not shown)
Reading the argument
What if the people who stretch are more likely to get injured in the first place?
Picture a younger runner who rarely thinks about stretching and an older runner who has dealt with injuries and takes more precautions. That is a possible difference between the groups, not a fact the study establishes. But the description doesn't tell us that the stretchers and nonstretchers began with equal injury risks.
If a higher-risk group stretches and finishes with the same number of injuries as a lower-risk group, stretching could be helping. Suppose the stretchers would otherwise have had twice as many injuries. Bringing them down to the other group's level would be an improvement, even though the final totals match. Equal outcomes don't automatically mean the precaution had no effect.
What we’re looking for
For a weakener, I'd look for evidence that the stretchers were more injury-prone to begin with. That would make the comparison a poor basis for declaring that stretching doesn't help.
Working the answers
- A
Both groups having fewer injuries than joggers overall doesn't tell us what stretching contributed. Perhaps everyone in the study was unusually careful. That could explain the low overall rates while leaving the stretchers-versus-nonstretchers comparison unresolved. We need something bearing on the difference the researcher is using to judge stretching.
- B
Previously injured joggers having difficulty performing stretches isn't the same as injury-prone joggers being more likely to stretch. This begins with a relevant group, but it doesn't tell us how that group is distributed between the two groups being compared. Nor does difficulty doing the stretches show that successful stretching prevents later injuries.
- C
This gives us a reason stretching might fail to prevent many injuries: flexibility may do little against falls or collisions. That fits the researcher's conclusion more readily than it challenges it. We need evidence of a possible benefit hidden by the comparison, not a reason the benefit might be limited.
- DCorrect
Injury-prone joggers are more likely to adopt the stretching habit. Now we have the group difference our prediction needed. The people stretching tend to be those with greater initial risk, so matching the other group's injury total could reflect a reduction from a worse starting point. The researcher treats the groups' equal outcomes as though their risks were equal before stretching, and D gives us reason to doubt that.
- E
There are two gaps. “Certain forms of exercise” needn't include jogging; the studies could concern another activity. And reducing the severity of injuries isn't the same as preventing injuries from occurring. A jogger could suffer just as many injuries, but milder ones. That would be a benefit, yet it wouldn't directly challenge this conclusion about preventing jogging injuries.
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