PrepTest 124, Section 2, Question 8
Travel writer: A vacationer should choose an airline(51 more words not shown)
The flawed reasoning in the(15 more words not shown)
- AA tossed coin(39 more words not shown)
- BIf there are(61 more words not shown)
- COn a given(46 more words not shown)
- DThe average adolescent(61 more words not shown)
- EThough until recently(56 more words not shown)
Reading the argument
An airline has avoided accidents, so now we should avoid the airline? I'd want a much better reason than that.
The statistic describes an average. It doesn't tell us that every airline has the same safety record. Maybe one airline avoids crashes because it follows unusually careful safety procedures, while another has accidents much more often. An average across airlines doesn't tell us which kind of airline we're considering.
The writer takes that general statistic and uses it to make a prediction about an airline that hasn't crashed recently. But its clean record might reflect something about that airline, rather than a reason to think its risk has increased.
What we’re looking for
We're looking for the same flaw in another argument. I'd begin by looking for an average being applied to an individual without accounting for relevant differences. Then check the whole inference, especially what the argument claims follows from the individual's past record.
Working the answers
- A
This uses a coin's unusual record to suggest that the coin itself may be biased. The conclusion predicts more of the same outcome: more heads. It doesn't claim that an outcome becomes more likely because it hasn't happened for a long time. Nor does it apply a group average to an individual coin in the way the airline argument does.
- BCorrect
The average baboon's one-in-ten chance plays the role of the average airline's accident rate. A particular baboon has gone years without becoming dominant, just as an airline has gone years without a crash. The argument then claims that the missing event has become more likely.
But waiting doesn't establish improved odds. Perhaps this baboon is much smaller than the others and remains unlikely to become dominant. Its history could reflect that continuing disadvantage, just as an airline's clean record could reflect continuing safety practices. Neither average proves that an individual is now due for the event.
- C
This does apply a group average to one individual, so it resembles the concern we first noticed. A five-year-old's circumstances could differ from an average resident's. But the conclusion simply assigns Marty the average risk. It never says Marty has avoided accidents for a long time and is therefore more likely to have one now. B matches that extra step as well.
- D
This compares earnings: part-time adolescents earn less than full-time adolescents, who earn less than full-time adults. The final comparison then shifts from full-time adults to employed adults generally, a group that could include part-time workers. That is a change in the comparison group. It isn't the airline argument's claim that an event becomes more likely because it hasn't happened for a long time.
- E
The chess argument uses one player's recent behavior to predict that player's next move. It predicts the recent pattern will continue; it doesn't claim a missing move must become more likely to compensate for not happening. The old and recent percentages are also about the same player, not a group average applied to a member.
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