Beware of interviewer bias. Whenever a researcher has direct contact with participants, even over the telephone, there is a risk that the researcher will influence their natural responses. On the telephone, the primary problem is exerting influence by tone of voice or by rephrasing questions. The standard solutions are to practice reading the survey questions in a consistent, neutral tone, and never to alter a survey questions. If a participant does not understand a question and asks for clarification, your only option is to reread the question. If you paraphrase a question or try to explain what it means, then you have changed the question and maybe even changed the participant's answer. Consider the following two versions of the same question. The first uses neutral wording and focuses on the library hours. The second question is phrased in a leading way; that is, it appears to be an invitation for the participant to join a happy little group (especially if the question is read in a very friendly tone of voice).