ABSTRACT
Ireland, 'Islands in the British Seas', 'at sea' and abroad (a typical lay-out is shown in Table 4.1). These enumerations were divided by sex from 1861 and between 1851 and 1871 inclusive into 'under 20' and '20 or over' age groups. Migrant age structure is not only important in its own right, as one of the most common migration differentials, but also, because it enables the mortality of migrant groups to be estimated, it is an important tool of analysis.16 Unfortunately, before 1911 no comparable data on migrant age structure were tabulated, and then only for four counties (three in Wales) and selected towns.
