Bias is a type of error that occurs because of t he background, expectations, or perceptions of the observer. Contamination occurs when the observer has knowledge of one or more aspects of the study and this knowledge affects subsequent observations. The Halo effect occurs when an observer allows an initial impression about one aspect of a person or group to influence observations on other aspects. The interview is a form of data collection in which questions are asked orally and subjects' responses are recorded. There is direct verbal interaction between the interviewer and the respondent.
Structured questions give the subject choices from which an answer is selected.
The interviewer has a great goal in mind and asks questions relevant to this goal. Thus, there is some latitude in what is asked, and often somewhat different questions are used with each subject. Semi structured questions do not have a predetermined, structured choices. Rather, the question is open-ended yet specific in intent, allowing individual responses. The ideal role of the interviewer is to act as a neutral medium through which information is transmitted.