To determine how many people in the Dutch population say they belong to a certain religion or ideology, every year 10 thousand people are asked: ‘Which religion or ideology would you say you belong to?” The answer categories are: ‘none’, ‘Roman Catholic’, ‘Dutch Reformed Church’ ‘Calvinist Church’, ‘Protestant Church in the Netherlands’, ‘Islam’ and ‘other’. For children aged 0 to 11 years, the parents or guardians answer this question. Children aged 12 to 15 years may answer for themselves, but a parent may also answer for them. From the age of 16 everyone answers the question themselves. The question on religion is included in the permanent life situation survey (POLS). As the figures are based on a sample, they are subject to a margin of error. The sample is drawn from the Dutch population, excluding the institutionalised population.