Personal interviewing is most effective when all the people to be interviewed are located

in a relatively small geographical area. Otherwise, the time and expense spent in travelling from one person to another makes this type of interviewing economically impractical. Personal interviewing is usually used when the information needed is too complex to be gathered by another technique. For example, a problem being studied may require the interviewer to probe beyond the more superficial answers that might be obtained with another method.

It is sometimes assumed that personal interviewing is the most accurate of all survey research techniques. Although personal interviewing may be accurate in many cases, human errors may prevent a researcher from obtaining valid results. Questions perceived by the interviewee as an invasion of privacy or threatening in any way will probably produce false or partially true answers. Also, since the interviewer must interpret the respondent's statements, a certain amount of information lose results even though the respondent may be answering truthfully.

In spite of the problems, at least two major advantages are provided by this research technique. First, the alert interviewer can generally tell if the respondent is being truthful or if he or she is giving superficial or untrue responses. Second, the interviewer can rephrase questions, give more explanation, or probe more deeply if the initial questions do not produce the information desired. As a result, the information gleaned should be more accurate than that provided by interviews where no one is present to clarify questions or to interpret answers.

It can be concluded from the passage that when all the people to be interviewed are located in a relatively big geographical area______.

A．personal interviewing is most effective

B．personal interviewing is economically impractical

C．personal interviewing is the only technique to get information

D．telephone interviewing may not be used