‘Estimating with Confidence’ and hindsight: new UK small area population estimates for 1991

Population estimates are used in a variety of applications including the monitoring of social trends, the distribution of financial resources and assessment of demand for housing, schooling, employment and other goods and services. In many countries the primary source informing population estimates is a national census. A census, however, is not a perfect source. Even after imputation of missing households, the UK's 1991 Census counts were lower than expected. In the 1990s, the Estimating with Confidence project (EwC) distributed official non-response data for local authority districts on a small area-specific basis to allow for underenumeration, timing changes between census day and the mid-year, armed forces adjustments and the transfer of students from home to term-time addresses. The EwC-enhanced census counts became accepted as the ‘gold standard’ for mid-1991 small area populations and were widely used in research. Following the 2001 Census, evidence suggested that previous official upward adjustments to 1991 populations were too large. Revisions were retrospectively made to 1991 non-responses and to the official annual time-series of subnational mid-year population estimates. For the UK's small areas, here we have revised the original EwC non-response allowances, converted the output to more contemporary geographies, and extended the estimates detail to single year of age. As a result, the 1991 EwC small-area estimates are now consistent and comparable with the 2001 Census population definition and geography and the 1981–2001 official population time-series. Our revised UK-coverage small-area population estimates can underpin late twentieth century local-area social analyses. Given the very detailed geographical and demographic detail in the estimates, we recommend these resources are used as building bricks for aggregation to larger areas and to application-relevant age bands. We present example calculations to assess differences which occur when a revised population estimate is used for the calculation of population change and as the denominator in demographic rates. Re-worked research affects demographic, health and social indicators, especially the ranking of areas' population and population change, although the extent of the revisions often may not result in different conclusions being drawn about trends and patterns.