How small a population can be usefully projected? geography and ethnic group

Ludi Simpson, Cathie Marsh Centre for Census and Survey Research
Paul Norman, Cathie Marsh Centre for Census and Survey Research
Abdelouahid Tajar, University of Manchester

Estimates of natural growth and net migration have been derived from successive censuses for very small areas and each of six ethnic groups. A projection model is presented and evaluated. The local government authorities of Oldham and Rochdale in the North of England are concerned to provide appropriate housing, in partnership with a Housing Market Renewal programme. Due to boundary changes, only the least detailed data from the 1991 and 2001 censuses are available for the project. The age structure of each group provides estimates of births and deaths, while net migration is derived as residual population change. The projection model uses demographic rates based on age-specific populations at risk at the start of the decade, and headship rates specific to each area and ethnic group. The model is evaluated by comparing its results at different geographical scales, and by removing information about age-structure. Implementation within Excel includes automated mapping.