Question

a utility company hires pollsters to knock on random doors in different parts of town to survey residents about the cost of their electric bill. would this study be biased? why or why not?
no, it is not biased. all residents of the town will have the opportunity to respond.
yes, it is biased. some of the residents who are surveyed may not want to respond to someone who knocks at their door.
no, it is not biased. all residents who are surveyed will want to respond.
yes, it is biased. only certain parts of the town were surveyed.

Explanation:

Sampling bias occurs when the sample does not represent the entire population. Since only certain parts of the town were surveyed, the sample may not be representative of all residents in the town regarding their electric - bill costs.

Answer:

Yes, it is biased. Only certain parts of the town were surveyed.