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Question

Difficulty: MediumSampling and Survey Flaws

City transit official: To assess the public's satisfaction with the newly introduced Rapid Commute bus line, we surveyed commuters waiting at the line's busiest stops during the morning rush hour. Over 90 percent of the respondents indicated that the new bus line is highly convenient and significantly reduces their commute time. Clearly, the residents of this city overwhelmingly find the new Rapid Commute line to be a valuable and convenient addition to our transit system.

Which of the following most accurately describes a flaw in the transit official's reasoning?

  1. It bases a broad generalization about the city's residents on a sample that is inherently biased toward those who already use and benefit from the service.Answer
  2. B
    It treats evidence concerning the proportion of surveyed individuals who are satisfied as definitive evidence regarding the total absolute number of satisfied residents in the city.
  3. C
    It concludes that the new bus line is the primary cause of reduced commute times, when the evidence provided only establishes a statistical correlation between the two.
  4. D
    It treats a condition that is sufficient to make a commute convenient as a condition that is logically necessary for any convenient commute.
  5. E
    It relies on an ambiguous use of the term 'convenient', shifting its meaning illicitly between the survey responses and the final conclusion.

Answer

The argument bases a broad generalization about the city's residents on a sample that is inherently biased toward those who already use and benefit from the service.
The argument's conclusion makes a sweeping claim about 'the residents of this city' based entirely on a survey of people who were already waiting at the bus stops of the new line. This is a classic example of an unrepresentative sample (selection bias). People who actively choose to wait for a bus are much more likely to find it convenient than the general public. Those who find it inconvenient likely took a different form of transportation and were entirely excluded from the survey.

Step-by-Step Solution

1
Identify the main conclusion of the argument.
The conclusion is: 'Clearly, the residents of this city overwhelmingly find the new Rapid Commute line to be a valuable and convenient addition to our transit system.'
Locating the conclusion sets the scope of the argument, showing that the official is making a claim about ALL residents of the city.
2
Identify the premises provided to support this conclusion.
The premise is: Over 90 percent of commuters surveyed at the bus line's busiest stops during rush hour find the line convenient and time-saving.
Understanding the evidence reveals how the author attempts to justify the broad conclusion.
3
Evaluate the relationship between the premises and the conclusion to find the logical gap.
The evidence relies on a survey of people already waiting for the bus. People who do not find the bus convenient or useful are highly unlikely to be waiting at the bus stop.
This reveals a textbook sampling flaw (selection bias). The sample is completely unrepresentative of the broader group (all city residents) being discussed in the conclusion.
4
Select the option that best abstracts this specific vulnerability.
The correct option points out that the argument bases a generalization about a larger group on a biased, unrepresentative sample of users.
This perfectly matches the identified logical gap in the argument.

Key Concept

Identifying Unrepresentative Samples and Selection Bias
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Topics

Sampling and Survey Flaws

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