Passage 1
Personal interviewing is most effective when all the people to be interviewed are located in relatively small geographical area. Otherwise, the time and expense spent in traveling from one person to another makes this type of interviewin

Passage 1
Personal interviewing is most effective when all the people to be interviewed are located in relatively small geographical area. Otherwise, the time and expense spent in traveling 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(应试者) 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 loss 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.
31.Sometimes a researcher cannot get valid results because ______.

A.the information needed is too complex to be gathered

B.personal interviewing is the most accurate of all survey research techniques

C.personal interviewing is not as effective as other research techniques

D.both interviewer and interviewee may make mistakes during the interviewing

正确答案是D