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 not all members of the population have an equal chance of being included in the sample. In this case, only residents in certain parts of the town are surveyed, which means the sample may not be representative of all town - residents. Those in non - surveyed areas are excluded from the study, leading to bias.

Answer:

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