Survey research involves asking questions of respondents and can take the form of questionnaires or interviews. Questionnaires are usually self-administered paper surveys while interviews involve an interviewer asking questions based on a respondent's answers. There are various types of questionnaires including mail, group-administered, and drop-off surveys. Interviews can be telephone or in-person. Key considerations in choosing a survey method include the population's accessibility, literacy, language barriers, willingness to cooperate, and geographic distribution as well as the nature of the questions, content, potential for bias, costs, facilities, and time required.