2011 Census - Guidance note on the census estimates of those who have ever lived outside Northern Ireland

Northern Ireland has historically experienced net outward migration, and subsequently, there is interest in determining the extent to which people who leave Northern Ireland return to Northern Ireland (so-called returning migrants). To address this, the 2011 Census included a question, addressed to every usual resident, asking (Q10) ‘Have you ever lived outside Northern Ireland for a continuous period of one year or more?’. The question specified 'one year or more' because this is the basis of international definitions for migration and usual residence.