A random sample of adults in a large US city responded to a series of questions about their use of public transportation. The results of the survey showed that 520 of the 838 adults in the sample (62%) have used public transportation in the past week. How might the results of the survey be biased in obtaining an estimate of all US residents who use public transportation?
Answer
A
Because not all residents in this US city were asked to participate, the survey may underestimate usage of public transportation.
B
Because the sample includes only residents in one US city, the survey may overestimate the proportion of US adults who use public transportation.
C
Because those surveyed may choose not to answer, the survey may underestimate the proportion of US residents who use public transportation.
D
Because the survey includes a random sample of residents in one US city, the survey should provide an accurate estimate of the proportion of US adults who use public transportation.
Explanation
The sample was randomly selected from just one US city, but the estimate is meant to describe adults across the whole country. Public transportation use may be higher in that city than in the US overall, so the sample could overestimate the national proportion. Random sampling within one city does not make the sample representative of all US adults.
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