Depending on the country context, ethnicity, religion and language may reflect equivalent characteristics and may not therefore all be needed. Ethnicity can be measured using a variety of concepts, including ethnic ancestry or origin, ethnic identity, cultural origins, nationality, race, colour, minority status, tribe, caste, language and religion, or a combination of these concepts. Because of interpretative difficulties that can occur, it is important that the basic criteria used to measure concepts are clearly explained to interviewers and respondents. The method and the format of the questions used to measure ethnicity can influence the choices that respondents make regarding their ethnic background and ethnic identification. Because of the subjective nature of concepts and increasing intermarriage among groups in some countries, information on ethnicity must be acquired directly from respondents (as opposed to interviewers making that assessment based on personal appearance) and respondents must have the option of indicating multiple ethnic affiliations.