AWISS Data Sources

AWISS is based at Swansea University and utilises the Secure Anonymised Information Linkage (SAIL) databank (

SAIL is a large scale, privacy protecting system, which enables anonymised health, educational and social records at the individual and household level to be linked and analysed to support health related outcomes.  It is one of only six high-quality data linkage systems worldwide, and is unique in its ability to anonymise and link data at multiple levels.

Within SAIL, all Welsh residents are assigned a unique, non-identifying ‘Anonymised Linkage Field’, a 10 digit random number, which is linkable across datasets in SAIL.  In addition, anonymised linkage fields are assigned to every residence in Wales enabling residents who live together to be identified, maternal-child links enable children to be linked to their parents, and encrypted organisational codes are available for schools, healthcare facilities, and small area geographies.  Hence, it is possible within SAIL to embed individuals within multi-level hierarchies and evaluate simple or complex interventions, operating at several levels. The SAIL infrastructure also enables AWISS analysts to develop a better understanding of the complex causal pathways between injury exposures, interventions and outcomes.

AWISS has access to several anonymised datasets within the SAIL database (listed below) which can be linked and analysed to support epidemiological analyses and the evaluation of preventative interventions.

Emergency Department Data Set (EDDS)

The Emergency Department Data Set (EDDS) attempts to capture all activity at Emergency Departments (EDs) and Minor Injury Units in NHS Wales hospitals.

Data are collected and coded at each hospital, before being electronically transferred to the NHS Wales Informatics Service (NWIS), to be validated and merged into the main EDDS database. Diagnoses, treatments, mechanism, activity and location of injuries, are coded using broad categories. Further details can be accessed at:

Major (24-hour, consultant led) Emergency Departments begun submitting data from April 2009 and all other hospitals providing emergency care facilities have been providing data since April 2012.

Whilst EDDS should represent 100% of the attendances, not all units were able to submit data from the 1st April 2009 and therefore data may be incomplete for earlier time periods.  Further, although data checks are conducted by NWIS and Health Boards, these checks often focus on data validity rather than the accuracy of the coding used, and as such inaccuracies are present within the ED dataset.

Patient Episode Database for Wales (PEDW)

The Patient Episode Database for Wales (PEDW) records all episodes of inpatient and daycase activity in NHS Wales hospitals. This includes planned and emergency admissions, minor and major operations, and hospital stays for giving birth. Hospital activity for Welsh residents treated in hospitals in England is also included.

PEDW data are collected and coded at each hospital. The records are then electronically transferred to the NHS Wales Informatics Service (NWIS) where they are validated and merged into the main database before being anonymised and transferred to the SAIL database.

Diagnoses are coded using the International Classification of Diseases (ICD). Further details on ICD can be accessed:  Procedures are coded using the OPCS classification of surgical operations.

Whilst PEDW should be a complete record of all inpatient and daycase activity in NHS Wales, it is acknowledged by NWIS that errors will be present within the PEDW dataset.  However, as PEDW comprises around one million episodes of hospital care per year, only a small proportion of the data is affected.

See the  Public Health Wales Observatory website for further details:

Mortality Data from the Office of National Statistics (ONS)

The Office of National Statistics (ONS) mortality data set contains an annual extract of anonymised deaths data for Welsh residents.  The dataset contains details of the underlying cause of death, year of registration and year of occurrence. Injury related deaths can be identified in this dataset by searching for International Classification of Diseases (ICD) external cause codes in the underlying cause of death field.

See the ONS website for further details:

Welsh Demographic Dataset

The Welsh Demographic Service data set contains administrative information about individuals who live in Wales that use NHS services; such as address and practice registration history.  It replaced the NHS Wales Administrative Register (NHSAR) in 2009. This dataset provides linkage from anonymous individual to anonymous residences, thus enabling households of individuals to be grouped together.

See the WDS website for further details:

Primary Care General Practice (GP) dataset

The Primary Care GP dataset contains electronic health records for all patients attending GP practices that are signed up to the SAIL database (approx. 80% of GPs in Wales).

Each GP practice uses a clinical information system to maintain an electronic health record for their patients; capturing the signs, symptoms, test results, diagnoses, prescribed treatment, referrals for specialist treatment and social aspects relating to the patients home environment.

See the SAIL website for further details:

Welsh Centre for Burns Unit dataset

The Welsh Centre for Burns Unit (WCBU) dataset contains records on all assessments and admissions to the WCBU based in Morriston Hospital.   The unit serves a population of around 2.3 million Welsh residents from across South, Mid and West Wales.  Further in May 2010, the WCBU was designated as the Adult Burn Centre for the South West UK Burns Network, covering a population of around 10 million.   Complex burn injured patients from other parts of the UK can also be referred to the Welsh Centre for Burns via the National Burns Bed Bureau. The unit treats around 750 burns patients a year, of which half need inpatient treatment. It also treats over 6,500 plastic surgery cases. Approximately half are children. While the team treats children with moderately severe burns, those with more extensive injuries are transferred to the paediatric burn centre in Bristol.

See the WCBU website for further details:

Critical Care Minimum Data Set (CCMDS)

The CCMDS was incorporated into SAIL in 2015 and AWISS staff have recently began exploring the utility of the data set. The CCMDS contains 34 fields which provide key administrative and clinical data approved for collection by NHS Trusts admitting adult patients who require level 2 or 3 critical care.

See the Health and Social Care Information Centre website for further details: