A guide to
Middle Super Output Areas (MSOAs)
Blaenau Gwent LHB
Copyright © 2008 National Public Health Service for Wales
Typographical Copyright © 2008 National Public Health Service for Wales
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1 Introduction
In a recent series of documents produced to assist Local Health Boards (LHBs) with the health needs assessment part of the Health, Social Care and Well-being Strategies, the Health Information Analysis Team presented a number of indicators at Middle Super Output Area (MSOA) level.
In response to requests for further information regarding this new geography, this document aims firstly to clarify the rationale for using MSOAs to report small area statistics. This is followed by a series of maps to show how MSOAs relate to electoral divisions in Blaenau Gwent.
1.1 Difficulties associated with reporting health data by electoral division
Traditionally, small area statistics have been reported at electoral division (or ward) level. Electoral divisions are administrative units which are used for the purpose of local government. The advantage of presenting data at this geography is that it is understood at local level and, of course, delineates the areas represented by councillors. There are, however, disadvantages which make electoral divisions less suitable for presenting some types of data, particularly health data.
Firstly, since electoral divisions are an administrative geography, the Boundary Commission for Wales frequently alter boundaries to ensure fair democratic representation. This makes the presentation of data covering a number of years difficult and prone to error.
Secondly, and most importantly, electoral divisions are heterogeneous in terms of their population size. In Wales there are just under 900 electoral divisions. Their populations range from less than a thousand persons to over 15 thousand. It is impossible to present reliable data on health for very small populations because the number of events, for example deaths, occurring in such areas will be relatively small. When this is the case, numbers tend to fluctuate considerably over time making it very difficult to determine whether the pattern exhibited is genuine or merely a chance occurrence.
1.2 The new statistical geographies
In order to try to overcome some of these problems, the Office for National Statistics (ONS) has created a new geographic hierarchy for England and Wales called Super Output Areas (SOAs).
The base units for the reporting of Census data are output areas, of which there are 9,000 in Wales. These output areas are grouped to form three levels of SOA: lower, middle and upper.
Lower Super Output Areas (LSOAs)
· Released in February 2004
· Total of 1896 in Wales, mean population 1500, minimum 1000
· Constrained by the boundaries of standard table electoral divisions used for 2001 Census outputs
· Take into account social homogeneity
Middle Super Output Areas (MSOAs)
· Released in August 2004
· Total of 413 in Wales, mean population 7500, minimum 5000
· Built from groups of LSOAs and constrained by the 2001 Census local authority boundaries
Upper Super Output Areas (USOAs)
· Release date: to be confirmed
· Mean population approx 25000
The ONS has stated that SOAs will be fixed for at least 10 years. So, the advantage of using these new statistical geographies is both stability and homogeneity. However, the main drawback is that they do not relate to local democracy and, at present, they do not have names. This makes them less amenable to the public and local government.
1.3 The NPHS position
The choice of geography used to present health data is firstly dependent upon the availability of data. However, the preference is always to use a statistical geography because by definition, they have been designed specifically with the aim of enabling the clear, consistent and reliable presentation of small area information.
The NPHS has thus concluded that the MSOA geography represents the best compromise between acknowledging the need for small area data and at the same time ensuring that the data, and hence any conclusions drawn, are robust. Nevertheless, where it is deemed appropriate, some data will continue to be presented by electoral division.
The NPHS is aware that the presentation of data at MSOA level will affect different Local Health Boards (LHBs) in different ways. In rural areas, since they have a minimum population of 5000, MSOAs will sometimes span five or more geographically large but sparsely-populated electoral divisions; this will result in some LHBs having far fewer MSOAs than electoral divisions (see appendix 1), and there will be less definition to outputs presented at MSOA level within such areas. As areas become more urban, the number of MSOAs will more closely compare to the number of electoral divisions; in the case of Cardiff, the use of MSOAs will provide greater definition to the presentation of data than is the case with electoral divisions (see appendix 1).
Version: 2a / Date: 05/02/2008 / Status: FinalAuthor: Hugo Cosh / Page: 1 of 10
National Public Health Service for Wales / A guide to Middle Super Output Areas
2 Map of electoral divisions in Blaenau Gwent
3 Map of Middle Super Output Areas (MSOAs) in Blaenau Gwent
4 Map of electoral divisions overlaid with MSOAs in Blaenau Gwent
Version: 2a / Date: 05/02/2008 / Status: FinalAuthor: Hugo Cosh / Page: 1 of 10
National Public Health Service for Wales / A guide to Middle Super Output Areas
Appendix 1: Number of electoral divisions, MSOAs and LSOAs in Wales LHBs
Appendix 2: Key to maps
Version: 2a / Date: 05/02/2008 / Status: FinalAuthor: Hugo Cosh / Page: 1 of 10