A popular website places opinion poll questions next to many of its news stories. Simply

click your response to join the sample. One of the questions was “Do you plan to diet this

year?” More than 30,000 people responded, with 68% saying “Yes.” Which of the

following is true?

a. About 68% of Americans planned to diet.

b. The poll used a convenience sample, so the results tell us little about the population of

all adults.

c. The poll uses voluntary response, so the results tell us little about the population of all

adults.

d. The sample is too small to draw any conclusion.

e. None of these.

We need to find the true statement from the given statements.

(a) Not true, because the sample is not typical of the total American population because only those with the strongest beliefs actively replied to the poll, and hence the proportion is most likely wrong for the entire population.

(b) Not true, since convenience sampling selects a subset of the population that is convenient for the sample, which is not the case here.

(c) True, because a voluntary response sample is one in which subjects may choose whether or not to participate in the study, and respondents have to willingly answer in this sample.

(d) Not true, because $30,000$persons is a relatively big sample size (not small).

(e) Not true, because we have established that response choice (c) was correct.