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:

In a survey, bias can occur when the sample is not representative of the population or when there are factors that influence responses. Here, some residents may not want to respond to a door - to - door pollster. This non - response can skew the results and introduce bias. Just because all residents have the opportunity to respond doesn't mean they will, and not all parts of the town being surveyed isn't the main source of bias here as it's random parts. Also, assuming all surveyed residents will want to respond is unrealistic.

Answer:

Yes, it is biased. Some of the residents who are surveyed may not want to respond to someone who knocks at their door.