The following tables give Census data on employment change in Preston and should be consulted for much of the discussion in Chapter 4. It is however a difficult matter to put together a set of tables analysing change over time, since the headings under which the data are classified change considerably over the period 1891–1951. In particular, up to 1911 the main classification is industrial, with workers being classified by the industry in which they work, though the more numerous sectors are often broken down by occupation as well. Tables A.I and A.2 give the details for change in Preston between 1891 and 1911, but many changes in classification have taken place which involve some reworking of the tables, as specified therein. From 1921 however occupational tables become available, and these are easier to use than the industrial tables, but In order to analyse change from 1911to1921 – a key period because of the impact of World War I on employment patterns – the 1911 tables have to be extensively reworked – by no means a perfect solution. The reworked data are presented in Table A.3. Finally, Table A.4 uses occupational Census data, again adjusted for comparability, to examine change from 1921 to 1951, but because no Census was taken in 1941 the table is an imperfect guide to the situation obtaining in the late 1930s.