According to the most recent estimates (1998), about 92% of the population is nominally Roman Catholic. However, Church officials report that only about half of these members are active practitioners. The next largest organization is the Church of Ireland, with a membership of about 3% of the population. About 0.4% of the population are Presbyterian, 0.1% are Methodist, and less than 0.1% are Jewish. There are small communities of Muslims and Jehovah's Witnesses. For ecclesiastical purposes, the Republic of Ireland and Northern Ireland (UK) constitute a single entity. Both Roman Catholics and Episcopalian churches have administrative seats at Armagh in Northern Ireland. The Presbyterian Church has its headquarters in Belfast.