Patient Episode Database for Wales (PEDW)

Data Providing Organisation:
NHS Wales’ Informatics Service (NWIS)

Data Providing Type:
Administrative (mandatory) data return



NHS Wales hospital admissions (Inpatients and daycases) dataset comprising of attendance and clinical information for all hospital admissions: includes diagnoses and operations performed.

Data Collection Method

The data are collected and coded at each hospital. Administrative information is collected from the central PAS (Patient Administrative System), such as specialty of care, admission and discharge dates. After the patient is discharged the hand written patient notes are transcribed by clinical coder into medical coding terminology (ICD10 and OPCS).

Data Highlights

The data held in PEDW is of interest to public health services since it can provide information regarding both health service utilisation and also the incidence and prevalence of disease. However, since PEDW was created to track hospital activity from the point of view of payments for services, rather than epidemiological analysis, the use of PEDW for public health work is not straightforward. For example:

  • Counts will vary depending on the number of diagnosis fields used e.g. primary only, all fields;
  • There are a number of different things that can be counted in PEDW e.g. individual episodes of care, admissions, discharges, periods of continuous care (group of episodes), patients or procedures.
  • When looking at diagnosis or procedures the number will vary depending on whether you look at only in the primary diagnosis / procedure field or if the secondary fields are also included.

Coding practices vary. In particular, coding practices for recording secondary diagnoses is likely to vary for different hospitals. This makes regional variations more difficult to interpret. The validation process led by the Corporate Health Improvement Programme and implemented by NWIS is aiming to address some of these inconsistencies.

Due to the complexity and pitfalls of PEDW it is recommended that any PEDW requests for public health purposes are discussed with a member of the SAIL team. In turn the SAIL will seek advice from NWIS if required.

Access Requirements

As a core SAIL dataset available in accordance with our standard Information Governance procedure.

More Information

See the PEDW website for more information and to view their published reports.


Approx. 950,000 hospital admissions per year

Data Level

Individual person

Data Years

1997 – Present

SAIL Schema