Differences in health area data

Figures in the Standard Tables for some Primary Care Trusts (PCTs) may differ from those in the Key Statistics and Census Area Statistics (CAS). This occurs where the PCTs comprise of wards which were not legally in existence on 31 December 2002. Exact figures were not produced for these PCTs to avoid the risk that confidential Census information about people might be deduced by comparing standard sets of statistics for overlapping areas.

The method of building appropriate figures differed between the Key Statistics/CAS and the Standard Tables because there were higher minimum populations, or confidentiality thresholds, for the release of the more detailed Standard Tables than for the simpler Key Statistics or CAS. For the affected PCTs, Output Areas - the smallest building brick for which Key Statistics and CAS are released - were fitted to the PCT boundaries for the production of Key Statistics and CAS so that these were as precise as possible. But larger building bricks - the 31 December 2002 wards - were fitted to the PCT boundaries for the production of Standard Tables. This often resulted in a difference between the two 'best fit' geographical definitions. The use of these standard building bricks avoided the disclosure risk arising from overlapping areas. A list of the 85 PCTs where geographical definitions are best fitted is provided in an Excel spreadsheet.