Data on ethnicity should not be derived from information on country of citizenship or country of birth. The classification of ethnic groups also requires the inclusion of the finest levels of ethnic groups, self-perceived groups, regional and local groups, as well as groups that are not usually considered to be ethnic groups, such as religious groups and those based on nationality. Pre-coding or pre-classification of ethnic groups in closed-ended survey questions may result in a loss of detailed information on the diversity of a population.