Vineetk wrote:
Columnist: Thomas's book "Spirited" has exercised much influence on a great numbers of this newspaper's readers. 2000 readers were surveyed and asked to name the book that had influence on their life. The book chosen most was the "Secret" and "Spirited" was second.
Which of the following question will be most useful in evaluating the columnist's argument?
A. How many people read the columnist’s newspaper?
B. How many books had each person surveyed read?
C. How many people chose books other than "Spirited"?
D. How many of those surveyed had actually read the books they chose?
E. How many books by Thomas other than "Spirited" were chosen?
Biased sample is very common in GMAT.
Description of the fallacy: Drawing a conclusion about a population based on a sample that is biased, or chosen in order to make it appear the population on average is different than it actually is.
Logical Form:
Sample S, which is biased, is taken from population P.
Conclusion C is drawn about population P based on S.There are
two main ways that a sample can fail to sufficiently represent the population:
1. The sample is simply
too small to represent the population.
2. The sample is biased in some way as a result of
not having been chosen randomly from the population. It illustrates that even a very large sample can be biased;
In short, for any sample, the important thing is representativeness, not size.Questions to evaluate a sample:When you see/hear a statistic, ask two questions:
(1) The sample is LARGE enough?
(2) The sample has been chosen RANDOMLY?ANALYZE THE STIMULUS:Fact: 2000 readers were surveyed and asked to name the book that had influence on their life.
Fact: The book chosen most was the "Secret" and "Spirited" was second.
Conclusion: Thomas’s book "Spirited" has exercised much influence on a great numbers of this newspaper's readers.
Question: Which of the following question will be most useful in evaluating the columnist's argument?
APPLY THE TECHNIQUE:Ask 2 questions:
(1) The number of people who voted for “Spirited” is
large enough?
(2) The readers were
chosen randomly or just people who are fan of Thomas?
ANALYZE EACH ANSWER:A. How many people read the columnist’s newspaper?
Wrong. The conclusion just says the book “Spirited” influences a great number of readers. In fact, 2000 people is a great number. If the book actually influences 2000 people, the conclusion is correct. Thus, A does not help.
B. How many books had each person surveyed read?
Wrong. The number of book that people read does not matter, if the “Spirited” influences them the most.
C. How many people chose books other than "Spirited"?
Correct. C attacks the conclusion by questioning that the number of people who chose “Spirited” is large enough to make conclusion? However, C uses other technique by questioning the rest of the sample, rather than the main object (the number of people read the “Spirited”).
The number of people read other book = Total number of people in the sample – number of people read “Spirited”. Thus, C does help.
D. How many of those surveyed had actually read the books they chose?
Wrong. It does mean one is influenced by the book only if he actually reads it. There are many aspects of the book can influence a person such as the author, the name of book, etc…..
E. How many books by Thomas other than "Spirited" were chosen?
Wrong. It does not matter. Even when there are many books by Thomas were chosen, the “Spirited” may influence the most if it is representative enough.
Hope it helps.