If born outside England or Wales, however, only the country is generally given. When using the census it is important to remember that members of the family who were not sleeping at home on the night of the census are not recorded with their family. A missing person in a family group in any of the census returns could be explained by the fact that the person was in hospital, in prison or in service. There is a much more realistic chance of tracing back several generations when searching censuses for a rural community, than there is an urban community. However, the next best thing is to find a common ancestral link in the urban community giving a rural birthplace.
Unusual occupations can occasionally indicate the same link between families.
The original books are held by the Public Record Office in London and the information is released by the Public Record Office after a hundred years. The data was released county by county on microfiche during the 1990s, with a national surname index appearing in late 1998. In summer 1999 the CD- ROM version was launched, consisting of 16 regional disks and a national name index on a further 8 disks. Altogether, the dataset comprises information for over 30 million individuals.