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Publication, Part of

Hospital Outpatient Activity 2019-20

National statistics

National Statistics

Data Quality Statement


HES data includes patient level data on hospital admissions, outpatient appointments and A&E attendances for all NHS trusts in England. It covers acute hospitals, mental health trusts and other providers of hospital care. HES includes information about private patients treated in NHS hospitals, patients who were resident outside England and care delivered by treatment centres (including those in the independent sector) funded by the NHS.

Healthcare providers collect administrative and clinical information locally to support the care of the patient. This data is submitted to SUS to enable hospitals to be paid for the care they deliver. HES is created from SUS to enable further secondary use of this data.

HES is the data source for a wide range of healthcare analysis used by a variety of people including the NHS, government, regulators, academic researchers, the media and members of the public.

HES is a unique data source, whose strength lies in the richness of detail at patient level going back to 1989 for Admitted Patient Care (APC) episodes, 2003 for outpatient appointments and 2007 for A&E attendances. HES data includes:

  • specific information about the patient, such as age, gender and ethnicity
  • clinical information about diagnoses, operations and consultant specialties
  • administrative information, such as time waited, and dates and methods of admission and discharge
  • geographical information such as where the patient was treated and the area in which they live

The principal benefits of HES are in its use to:

  • monitor trends and patterns in NHS hospital activity
  • assess effective delivery of care and provide the basis for national indicators of clinical quality
  • support NHS and parliamentary accountability
  • inform patient choice
  • provide information on hospital care within the NHS for the media
  • determine fair access to health care
  • develop, monitor and evaluate government policy
  • reveal health trends over time
  • support local service planning

The HES publications focus on headline information about hospital activity. Each annual publication includes a series of national tables and also provider-level breakdowns for some main areas.

Most data included in the published tables are aggregate counts of hospital activity. Where averages are published, e.g. average length of stay for inpatients or caesarean rates for maternity statistics, this data is clearly labelled stating how the data has been calculated.

Accuracy and Reliability

The accuracy of HES data is the responsibility of the NHS providers who submit the data to the Secondary Uses Service (SUS). This data is required to be accurate to enable providers to be correctly paid for the activity they undertake.

SUS is the single, comprehensive repository for healthcare data in England which enables a range of reporting and analyses to support the NHS in the delivery of healthcare services.

When a patient or service user is treated or cared for, information is collected which supports their treatment. This information is also useful to commissioners and providers of NHS-funded care for 'secondary' purposes - purposes other than direct or 'primary' clinical care - such as:

  • healthcare planning
  • commissioning of services
  • national tariff reimbursement
  • development of national policy

SUS is a secure data warehouse that stores this patient-level information in line with national standards and applies complex derivations which support national tariff policy and secondary analysis. 

A list of mandatory and optional fields for submission in in the Commissioning Data Set (CDS) is provided within the NHS Model and Data Dictionary:

Outpatients CDS V6-2 Type 120 – Outpatients CDS

NHS Digital has a well-developed data quality assurance process for the SUS and HES data. It uses an xml schema to ensure some standardisation of the data received. The use of the schema means that the data set has to meet certain validation rules before it can be submitted to SUS. NHS Digital leads on the schema changes and consults the data suppliers about proposed changes.

Each month NHS Digital create data quality dashboards available to NHS providers to show the completeness and validity of their data submissions to SUS. This helps to highlight any issues present in the provisional data allowing time for corrections to be made before the annual data is submitted.

An external auditor, acting on behalf of the Department of Health (DH), audits the data submitted to SUS to ensure NHS providers are being correctly paid by Payment by Results (PbR) for the care they provide.

NHS Digital validates and cleans the HES extract and derives new items. The team discusses data quality issues with the information leads in hospital trusts who are responsible for submitting data. The roles and responsibilities within NHS Digital are clear for the purposes of data quality assurance, to assess the quality of data received against published standards and report the results.

Data quality information for each year to date HES dataset is published alongside the provisional year to date HES data, and also alongside annual publications. These specify known data quality issues each year and where a trust has a known shortfall of secondary diagnoses. The statisticians can only check the validity and format of the data and not whether they are accurate, as accuracy checking requires a level of audit capacity and capability which NHS Digital does not currently possess.

Learn more about HES data quality 

NHS Digital also publishes an annual report The Quality of Nationally Submitted Health and Social Care Data, which highlights issues around the recording of the underlying data that is used for HES, as well as examples of good and poor practice, and a regular Data Quality Maturity Index.

Data Quality Note

Learn more about detailed information about data quality of data items, and completeness of provider data submissions.

Outpatient HES data has been available since 2003-04 and during those early years data completeness was known to be an issue.

Records submitted into the outpatients dataset are not required to populate diagnosis or procedure fields. As a result these fields will often show NULL values.


Data Completeness

The HES Outpatient 2019-20 data set includes records of patient appointments collected from 1,486 providers in England.

Table 1 shows the count and percentage of certain key fields in the outpatient data set that have valid values in 2018-19 and 2019-20.

Table 1: Data completeness for outpatient HES, 2018-19 and 2019-20




Outpatient key fields

Number of valid records

Percentage of all records

Number of valid records

Percentage of all records

Attendance type





Source of referral










Main specialty





Treatment specialty





Total appointments





Primary diagnosis*





Main procedure*





Total attended appointments





Source: NHS Digital

Final and Provisional Data Comparison

Collection of HES data is carried out on a monthly basis throughout the financial year, with a final annual refresh (AR) once the year end has passed. Each monthly collection refreshes data back to the start of the financial year.

Providers are no longer routinely offered the opportunity to re-submit data for HES after the submission deadline (top-up files), which was approved by partners on the Data Quality Steering Group (DQSG).  This has enabled us to commit to publishing Annual data earlier than for previous years.  Providers were informed about this decision emphasising the importance to submit data correctly before the inclusion date of 20 May 2019.

Users should note there was a reduction in appointments from March 2020, at the start of the COVID-19 outbreak.

Whilst NHS Digital encourages providers to submit all relevant data, Some providers only submit outpatient records for those appointments that were actually attended. Care should therefore be exercised when looking at the number of appointments that were labelled as cancelled or did not attend as these are likely to be an undercount of the actual position.


Table 2 shows the number of attended and did not attend appointments in month 13 and at annual refresh.

Table 2: Comparing month 13 and annual refresh data, 2019-20


Month 13

Annual refresh

Percentage change

Attended appointments




(Percentage of all appointments)




Did not attend appointment




(Percentage of all appointments)




Follow up attendances for each first attendance




Total appointments





Source: NHS Digital

Table 3 shows the change from the Months 12 and 13 provisional data and the final annual refresh data.

Table 3: Monthly variation in submitted records, 2019-20


Month 12

Month 13

Annual Refresh

Apr 2019




May 2019




Jun 2019




Jul 2019




Aug 2019




Sep 2019




Oct 2019




Nov 2019




Dec 2019




Jan 2020




Feb 2020




Mar 2020







Source: NHS Digital


Timeliness and Punctuality

HES data are published as early as possible. The production of the underlying annual HES data sets takes several months after the reference period. The final submission deadline for NHS providers to send annual data to SUS is normally at the end of May, almost two months after that year has finished. It then takes approximately two months to produce the HES APC data set and a further two months to complete publication production and data investigation.

In addition to annual data NHS Digital also publish provisional monthly HES data approximately two months after the reference period.

The final annual data includes additional data cleaning, validation and processing than the provisional monthly data.

UK Comparisons

Separate collections of hospital statistics are undertaken by Northern Ireland, Scotland and Wales. There are a number of important differences between the countries in the way that data measures are collected and classified, and because of differences between countries in the organisation of health and social services. For these reasons, any comparisons made between HES and other UK data should be treated with caution.

ONS used to produce UK Health Statistics which contained key figures about the use of health and social services, including hospital admitted patient activity and waiting times across the UK. 

Other UK Data

Hospital data for the other administrations can be found at: 

NHS England also publish hospital activity data


Wider International Comparisons

HES and similar statistics from the devolved administrations are used to contribute to World Health Organisation (WHO), Organisation for Economic Co-operation and Development (OECD) and Eurostat compendiums on health statistics.

Improvements over time

HES data is available from 1989-90 onwards whilst outpatient HES data is available from 2003-04 onwards, and A&E data is available from 2007-08. Changes to the figures over time need to be interpreted in the context of improvements in data quality and coverage (particularly in earlier years), improvements in coverage of independent sector activity (particularly from 2006-07) and changes in NHS practice.

Payment by Results (PbR) is a system whereby hospitals are paid for the number of patient treatments, known as activity, they perform and the complexity of these treatments. It was introduced in a phased way from 2003-04 onwards. In order to be paid correctly, care providers need to record the activity they perform and the clinical codes that outline the patients’ conditions and treatment.

The introduction of PbR increased private sector involvement in the delivery of secondary care and brought about some changes in clinical practice (including some procedures occurring as outpatient appointments instead of hospital admissions). It is likely that these changes will have affected trends.

This has provided a major financial incentive for care providers to ensure all of the activity they perform, and the clinical coding is fully recorded. This improved recording of information captured by HES could be one of the factors leading to the reported activity increases.

In order to manage patients’ waiting times there has been the need for additional elective operations to be performed as well as a requirement for more capacity in NHS funded care to perform this activity. In the middle of the last decade, additional capacity was brought in from the private sector via treatment centres, with the NHS funding some patients to be treated there for routine operations.

Improvements in technology and the need to increase efficiency to allow more patients to be treated have led to a reduction in the length of time patients need to stay in hospital for certain planned operations. In particular, many operations that would have involved an overnight stay at the start of the period are now routinely performed as day cases. In addition, many operations where a patient would have been admitted to hospital at the start of the period are now routinely performed in outpatients. This has led to increases in day case rates and outpatient attendances over the period.

The recent period has also seen a rise in the number of emergency admissions. One factor contributing to this is likely to be the increased demand on health services from an ageing population. Alongside this there has been the introduction of observation or medical assessment units at many hospitals to which patients arriving in A&E departments are admitted, often for around a day, to enable observation and tests to be performed on them.

Last edited: 13 January 2022 10:52 am