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. An interviewer's physical characteristics, voice, dress and attitude can effect the interview.
Contamination can also occur if the interviewers have knowledge of facets of the study.
They should not be aware of which subjects are receiving special treatments or whether certain results will have positive benefits. 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 questionnaire is the most widely used type of measure in educational research. A questionnaire is a written document containing statements or questions that are used to obtain subject perceptions, attitudes, beliefs, values, perspectives, and other traits. Questionnaires are used extensively because they provide the best way of obtaining information for a wide range of research problems, from surveying of large populations to reactions to different instructional methods.