Statistical Wards, CAS Wards and ST Wards

Statistical Wards

In 2003 a policy was introduced across National Statistics to minimise the statistical impact of frequent electoral ward boundary changes, particularly in England. Under this policy any changes to English or Welsh ward boundaries promulgated (laid down in statute) by the end of a calendar year were implemented for statistical purposes on 1 April of the following year, irrespective of the year the actual change came into operation. The wards resulting from this policy were known as 'statistical wards'.

2003 statistical wards were accordingly those that were promulgated by 31 December 2002. In general they reflected actual electoral wards as at May 2003, but for 28 local authorities they also included boundary changes that were not operational until June 2004. Therefore, for any given year statistical wards in some local authorities were different to the statutory electoral wards because of the varying time lags between promulgation and operation dates of boundary changes.

In 2006 a change to the policy was agreed by the National Statistics Geography Group (NSGG). The 1 April implementation date is retained but it now relates to those administrative and electoral areas that are statutorily operative on 31 December of the previous calendar year (i.e. statutory electoral wards). As such, statistical wards no longer exist - the last set produced was 2005 statistical wards.

Census Area Statistics (CAS) Wards

Census Area Statistics (CAS) wards are used for 2001 Census outputs, including those available on the Neighbourhood Statistics (NeSS) website. In England and Wales they are identical to the 2003 statistical wards except that 18 of the smallest wards (all in England) have been merged into other wards to avoid the confidentiality risks of releasing data for very small areas. This has occurred to those wards with fewer than 100 residents or 40 households (as at the 2001 Census). There are a total of 7969 CAS wards in England and 881 in Wales.

Scotland also has CAS wards but these are created from best-fit Output Area (OA) aggregations to 2001 electoral wards. There are 1222 Scottish CAS wards, with a minimum size of 50 residents and 20 households. Note too that Scottish Census outputs use different ward codes to the ONS standard. A look-up file is available on the area names & codes page (link below).

In Northern Ireland 2001 Census outputs use the 582 electoral wards in existence at Census Day. There was no requirement to introduce specific CAS wards as all electoral wards exceeded the 100 residents / 40 households threshold. However, as in Scotland, Northern Irish Census outputs use different ward codes to the ONS standard. A look-up file is also available on the area names & codes page.

Standard Table (ST) Wards

Standard Table (ST) wards are those for which the 2001 Census Standard Tables are available. They are a further subset of the statistical wards such that those with fewer than 1000 residents or 400 households have been merged. This was required to ensure the confidentiality of data in the Standard Tables.

In England and Wales a total of 113 statistical wards have been merged to create the ST ward set. There are a total of 7932 ST wards in England and 868 in Wales.

Scotland's 1176 ST wards have the same minimum size thresholds but do not always correspond exactly with Scottish CAS ward boundaries - the GROS website provides more explanation.

In Northern Ireland it was decided that ward-level statistics would also be released for the 9 sub-threshold wards on the basis that the risk of disclosure would not be increased by doing so. Accordingly there are no ST wards in Northern Ireland.

Note about names of CAS and ST wards

When two or more wards are merged to create CAS or ST wards in England and Wales, the name given to the new (enlarged) ward is that of the largest of its constituent wards (in terms of population). For example, Cwm-y-Glo statistical ward (Gwynedd) has been merged with the larger Bethel statistical ward to create the Bethel ST ward. Data users must therefore be aware of which ward set they are using - in this case Bethel ST ward clearly covers a much larger area and population than Bethel statistical ward.

Further information

The area names & codes files page provides links to:

• Statistical, CAS and ST ward lists
• A list of those local authorities subject to boundary change in May 2004, as promulgated by 31/12/2002.
• Details of those 2003 statistical wards that were merged to create the CAS and ST wards.
• Look-ups between the usual electoral ward codes and those used in Scottish and Northern Irish Census outputs.

Note that whilst new sets of statistical wards will come into effect each April, the CAS wards and ST wards were one-off sets specifically defined for 2001 Census outputs.

What is an electoral ward? Information here

This page last revised: Friday, 15 February 2008