A system for storing, checking, manipulating, analysing and displaying data which are spatially referenced

A GIS is an information system where the data has a geographical dimension (you could ignore the G, hence an IS)

A Management Information System (MIS) which enables map displays of information

‘Spatial analysis’ systems concerned with quantitative procedures applied to locational problems

An integrated system distinguished by high levels of mapping capability and spatial analysis

Data storage, input, retrieval, mapping and spatial analysis … to support the decision making activities of an organisation (A GIS integrates data from a variety of sources and presents information to decision makers). A GIS may become a spatial decision support system (SDSS).

Introduction to GIS course and health data sets

GIS systems

A geographical information system (GIS) is a computer based tool which stores, integrates, analyses, models and displays information using maps. Part of the power of a GIS system, is in the ability of spatial analysis to reveal health patterns of which managers were not previously aware. Spatial analysis offers an alternative 'picture' to that of a spreadsheet, chart or report summary. A GIS system may assist Health Authorities, PCT's, Trusts and healthcare commissioners, for example, to better understand issues surrounding access to, and the delivery of health services. It can help improve the understanding of the spatial incidence of disease or ill health. It can help make better and more informed use of existing data sources and knowledge. A wide range of analysis may be carried out using a GIS approach. Typical areas in which a GIS can be of benefit include the point mapping of patients, aggregated analyses within different geographical areas, and the modelling of potential service delivery options.

Recent 'windows' based GIS, or mapping packages, are in many ways very similar to other PC packages such as word processors, spreadsheets, databases and presentation packages. Such desktop GIS have a similar feel and look, with pull down menus, tool bars, buttons to press and varied menu options. Windows GIS are intuitive and relatively easy to use.

The main difference in a GIS is in its geographical or mapping functionality. In technical terms, a GIS can be used to store, create, manipulate and analyse information that is spatially linked to a local area, and then show this information on an output map.

A GIS may be defined in a number of ways :

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GIS have the potential to benefit Public Health analysis and decision making in a number of ways. For example, GIS can help in the following areas :

Better understanding local populations Measuring the equality of access to and use of particular services Informing the Health Improvement Programmes and Local Modernisation Reviews

that Health Authorities, Primary Care Trusts, other health professionals and Local Authorities are required to develop to help address issues of health promotion and ill health prevention locally

Supporting issues of clinical governance at both Trust and primary care level using a range of mortality, secondary care and morbidity data.

Exploring the effect Primary Care Groups and Trusts are having on services. Assisting in service planning and development Conducting environmental impact assessments Providing an epidemiology tool

A health service GIS works by linking data to maps, via a geographical or spatial link. This spatial link could comprise of a point on a map, derived by linking a patient postcode to a grid reference. Alternatively, the spatial link could be a summary of data, aggregated to a geographical area, such as a census or electoral ward. Summary data for each ward can then be linked to the appropriate ward on a map.

The following illustration shows typically used health service geographical areas.These comprise of :

North West Health Authorities (2001) North West Local Authorities (2001) Census wards within a Health Authority (1991) Point location of postcodes within a Health Authority (2001)

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Requirements for using GIS within Public Health work

In order to use a GIS within Public Health analysis, we need to consider the requirements for hardware, software, data and training.

A. Hardware

In order to make the best use of a GIS system and its functionality, an up to date PC is recommended. For example, in 2002, a desktop tower PC with a Pentium IV processor, 128 MB of SDRAM, large hard disc, CD ROM drive, and as large a monitor as possible - 19” would be ideal. This is likely to cost around £1,500.

Additionally, access to a quality colour printer is required for paper printouts. Competitively priced A3 deskjet's are now on the market, and offer high print quality.HA's, though not PCT's, may well have available colour laser A4 printers.

B. GIS software

There are a number of windows based GIS systems on the market. Major market leaders include MapInfo and ArcView. Whilst many North West Health Authorities initially used Atlas GIS in the early 1990's, this product is no longer supported within the UK.

Which package you use is up to personal choice. However, if you have close links with a local University which uses Arc Info as a GIS, you may decide to standardise on Arc View, the PC version. If you have close links with say a City Council which uses MapInfo, you may wish to standardise on this package. Recent research has indicated that MapInfo has been chosen by 90% of Health Service users by 2001.

These Windows GIS packages come boxed, and do not include health service data or local maps. It is up to the user to specify what they include within the local system being developed. Whilst ‘ready to use’ GIS are advertised within the health service, these packages are both expensive and limited in flexibility.

MapInfo and ArcView cost approximately £1,000 for the base software package. Other add on software modules which may be considered would include a postcode converter such as MapInfo’s ‘Quick Address’ and a drive time analysis module or thematic mapper module. However, each add on piece of software typically costs another £1,000.

C. Training requirements

This training course aims to guide you through the range of Health Service based data sets available for use within a windows GIS package, and to demonstrate the use of MapInfo.

D. Health and mapping data sets

A vast range of health service and other data sets are readily available which can be presented and analysed using GIS software.

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The three main types of data used within health service spatial analyis are :

i. Geographical maps for use within a geographical information system.

ii. Data sets already aggregated and standardised to a set level (e.g. ward, Local Authority, PCG/PCT or Health Authority).

iii. Data sets detailing individual patients or residents within a Health Authority, PCT or Trust catchment area, which, through use of the patient postcode, enables data to be aggregated to any given spatial level (e.g. census or electoral ward, future 2001 census output area, enumeration district (ED), postcode area, PCG, LA, PCT or HA).

Information on data sets available for each of the above groupings follows.

Available NHS spatial data sets

i. Mapping and spatial data sets

A range of maps, boundary files and data sets are available for purchase by NHS organisations, or can be made available from local partner organisations. These include :

a. Boundary data

1991 census wards are readily available for all wards within the North West. NHSE and HA data analysis typically makes use of such census wards. 1991 census enumeration districts (ED’s) are also available. ED’s nest within wards.

Over time, Local Authorities adapt their ward boundaries, with electoral wards taking over from census wards. HA’s and PCT’s may be able to obtain updated electoral wards. For example, 1997 or 2000 electoral ward boundaries are required to map the IMD2000 deprivation indicators.

2001 census data should include census ward and output area boundaries - available during 2003.

PCG , PCT and other neighbourhood boundaries may be created locally using ‘head-up’ digitising within a GIS. Local sites could include chemical tip sites, sure start estate borders, and so on.

b. Ordnance Survey (OS) map data

The Ordnance Survey can supply inexpensive 1:10,000 and 1:50,000 colour raster map tiles for the UK. Major North West route data is also available relatively cheaply in vector format, although digitised at a far larger scale.

c. ONS postcode converters

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The NHS receives a postcode converter file within the ‘NHS organisational codes’ CD ROM. This electronic file allocates a grid reference, ward and HA code to a given postcode. Postcodes can be readily mapped to 100 metre resolution squares.

However, a new Office of National Statistics (ONS) postcoder – ‘gridlink’ - provides six digit x and y co-ordinates for postcodes within a given Health Authority, down to a one metre resolution. An annual gridlink licence will cost approximately £150 per HA area.

d. Aerial photography

Many Local Authorities have available aerial photography, which can be incorporated within a GIS. LA’s are able to pass such data onto key partner organisations for use within joint project work. Such photographic maps may be useful when looking at very local sites.

ii. Individual patient data sets

1. Health Authority or Hospital Trust individual patient records

a. Inpatient database patient records

Hospital Trust PAS systems (patient admission systems) contain a variety of datasets of potential use by Public health and other teams. Trust datasets are catchment based – they summarise activity for all patients attending that hospital, regardless of where the patient lives. Health Authorities receive copies of some of these data sets, on a resident basis - namely for residents who live within a set geographical area. PCT’s will in the future receive similar resident based data.

Commissioning or Contract Minimum Data Sets (CMDS) are key building blocks used to analyse secondary care inpatient and day case Trust activity. Each CMDS is a (complete) electronic record of an individual patient’s time in hospital, detailing and summarising what has happened to a patient during their time in hospital. Each inpatient record contains data on :

age, sex of patient referring GP, consultant Trust(s) where activity undertaken HA of residence, purchaser type of admission (e.g. elective inpatient - stay at least one night (booked in

advance) or non-elective (emergency admission), day case, specialty group diagnosis, subdiagnosis, secondary diagnosis type of operation and/or procedure undertaken length of stay, dates within hospital, episode number outcome, discharge destination geographical data such as postcode …….

Individual projects need to brainstorm and specify exactly what data is required. Data files may contain raw data for each patient record, or be pre analysed. For example, a decision could be made to focus on all finished episode patient records, within a time

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period for a specific condition and age group. Alternatively, first episodes could be analysed, or individual patients identified by first date of admission, and so on.

Raw data can then be tidied, standardised and statistically analysed. For example, different data sets may be linked using common fields of data, and, data may be aggregated to a variety of levels (e.g. by Trust, GP, condition, age or geographical area). Statistical analysis may be undertaken (e.g. counts of activity, crude rates, age standardised ratios, statistical significance, trend analysis, forecasting). Data may be geographically mapped through the use of a geographical information system (GIS).Each stage requires greater levels of analysis input, skills, experience and time.

b. Additional Trust data - A&E Data, Outpatient data etc

Trusts have a range of additional data sets. These include outpatient data, A&E attendances, specialist clinics, radiology data, CABG/PTCA patient activity, and so on.

2. Public health birth and death tapes data sets

Public Health Teams receive data on every resident within their area who is born or dies within a given time period. A variety of data is contained within each data set. The death tapes include information on underlying cause of death, personal details and home location. The birth tapes provide information such as birth weight, and family details. Individual postcodes can be aggregated to any geographical level.

3. FHSA patient registers

FHSA teams hold patient registers for every patient registered with GP. Such patient data includes age, sex, GP, Practice and home address. FHSA data provides an alternative population structure to other aggregated tables, and are frequently used.

4. Primary care Morbidity data

GP practices hold a wealth of primary care morbidity and other data, which is potentially available for analysis if downloaded electronically from GP systems. Data includes :

GP practice age/sex registers : GP practice clinical system data : e.g. patient Read coded data on diagnosis, illness,

drug interventions, lifestyles data. Disease group registers (e.g. diabetes or IHD registers)

MAAG teams collect some of this data from GP practices. Typically, for reasons of confidentiality it is not released, or it is not currently postcoded for GIS analysis.

5. Cancer registry data :

Regional Cancer Registries hold data on all individuals registered as having a cancer within their area.

6. Site location data

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HA’s have available listings for the location of GP practices, dentists, opticians and pharmacists. Hospital sites, and other health care bases may equally be mapped.

iii. Aggregated patient data sets

1. NHSE North West series of Small Area Databases (SAD)

The NHSE North West has issued a number of ‘Small Area Databases’ to Health Authorities through the 1990’s. SAD tables provide ward level summaries for key health indicators for all wards within the North West. Some comparative data may be analysed over time.

The latest SAD is for 2000. Data is based on 1991 census wards, using updated estimates for 1991 ward populations.

The small area databases include a variety of information on :

standardised mortality ratios (SMR's) for major causes of death (latest 1997-99), by set age band, sex and ward

major diagnoses and operations (latest for April 1998 to March 2000) mid year population estimates birth weights

Specific additional data has been included within individual year SAD, for example, long term limiting illness and CACI smoking rates.

2. Government agency data sets

a. ONS Neighbourhood statistics data

During 2000, the Office for National Statistics (ONS) have introduced a number of ward level and Local authority level data sets data through the internet.

Ward level data is available for the following topic areas (frequently used by our LA’s).

Economic deprivation – family credit, income support claimants Education skills and training – primary school pupils at stage 2, university admissions Work – jobseekers allowance, incapacity benefits, severe disablement, etc Indices of deprivation – IOLD 2000 Population and vital statistics – mid 1998 population estimates Health – attendance allowance claimants, disability living allowance

This data is additionally available at Local Authority level.

b. Indices of local deprivation

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In 2000, the DETR produced the latest indices of local deprivation (IOLD 2000) based on 1998 ward boundaries. The 2000 IOLD scores include an overall score and ward ranking, as well as income, employment, health, education, housing and access scores. The index supersedes the previous 1998 DofE Index of Local Conditions. In addition to these ward level data sets, many HA’s have a range of deprivation data available, including Jarman, Townsend, Carstairs and MINI scores.

c. Teenage conception data

Ward level teenage conception data is available from ONS. This is available for under 18’s for 1992-95, 95-97, 98, and for under 16’s for 1992-97.

d. Classifications of wards and ED’s

Geodemographic ‘Superprofile’ lifestyle indicators, based on 1991 census enumeration district areas, were purchased by the NHSE. Superprofiles are available at three levels including broad lifestyle groupings (‘have nots’, ‘thriving greys’, etc) and more specific target groups (e.g. ‘single mums living mainly in council flats’).

In 1996 ONS produced ward classifications for England and Wales. This data set clusters wards into particular groupings, e.g. suburbia, rural areas, inner city estates, deprived city area, and so on.

3. 2001 ONS census, & 1991 census

The 2001 census was held in April 2001. Final results, based around new postcode linked geographical output areas are due by 2003. A wide variety of data will be available from the 2001 census for use by Health teams. The NHSE plan to disseminate data to HA’s, along with GIS based map boundaries. Data from the 1991 census is still available.

4. Annual Public Health Common Data Set (now renamed the compendium of clinical health indicators)

The annual Public Health Common Data Set (PHCDS), now renamed the compendium of clinical indicators, provides a wide variety of indicators for each Health Authority and Local Authority in England and Wales. Comparisons may be made within a Region, with neighbouring HA's or LA's and with similar type areas (e.g. former coal mining industries).

A wide variety of data is collected within the PHCDS, on Health of the Nation, Public Health and health outcome indicators. Summaries include district comparisons on accidents, cancer, CHD, MI, fertility, morbidity and mortality indicators, and so on. The PHCDS come with their own very extensive guide. The latest version is for 2000.

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The HA summaries enable comparisons to be mapped between all districts in E&W, districts within a Region (e.g. the NW), similar districts (e.g. local rural or urban districts) and neighbouring districts.

5. Local Authority data :

A variety of additional data is potentially available from Local Authorities, Unitary Authority or City Council teams. Council Teams provide a valuable source for data on areas such as housing and homelessness, crime, accidents, education, environmental data, social services data, Crime and Disorder equity audit data.

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