PrepTest 126, Section 1, Question 9
Several major earthquakes have occurred in a certain(45 more words not shown)
Which one of the following,(6 more words not shown)
- AScientists do not(30 more words not shown)
- BMost other earthquake(27 more words not shown)
- CThe frequency of(12 more words not shown)
- DThere is considerable(17 more words not shown)
- EThere is presently(18 more words not shown)
Reading the argument
What if those electrical changes happen every day?
We know they were detected before each major earthquake in the region. We haven't been told how often they happened without an earthquake afterward. If officials get the same warning almost every day, what are they supposed to do—keep evacuating everyone?
Think of pointing out that the sun rose before every tsunami. That wouldn't make a sunrise useful for deciding when a tsunami was coming; sunrises also happen on ordinary days. Likewise, a signal appearing before every earthquake isn't enough if it also appears constantly when nothing happens.
What we’re looking for
We're asked to weaken the promise of this method. I'd look for evidence that the electrical changes aren't a reliable guide to when officials should evacuate. My first concern is false alarms: signals without the event we're trying to predict.
Working the answers
- A
We don't need to understand where a signal comes from for it to be useful. If it reliably indicated when an earthquake was coming, officials could use it while scientists continued investigating its cause. A questions the explanation of the electrical changes, not their reliability as a warning.
- B
A stronger connection than other methods have doesn't show the new method is reliable enough. But it doesn't undermine the method either. If anything, that comparison makes it look more promising. We need evidence against its usefulness, not a favorable comparison with other methods.
- C
More earthquakes could make a good warning system more valuable. It doesn't tell us whether this particular system works. The number of events and our ability to predict their timing are different issues.
- DCorrect
This finds a different reliability problem from the false alarms I predicted. Even when an earthquake follows the signal, the delay varies considerably. Suppose one signal comes a month before the quake and another only ten minutes before. The signal wouldn't tell officials which schedule they face.
That matters because the promise is to help decide exactly when to evacuate. A warning that something will happen eventually leaves a serious timing problem. D doesn't need to show that the electrical changes are completely useless; it weakens the particular promise the author makes for them.
- E
One station might be enough to cover the region. We aren't told that it misses important signals or cannot monitor the relevant area. And a method that promises to help could include plans to build additional stations. We'd need another fact to turn the current station count into evidence that the method won't work.
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