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Publication, Part of

NHS Maternity Statistics, England - 2020-21

Official statistics

Data quality statement (HES)


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 the 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:

  • CDS V6-2 Type 120 – Finished Birth Episode CDS
  • CDS V6-2 Type 140 – Finished Delivery Episode CDS
  • CDS V6-2 Type 150 – Other Birth Event CDS
  • CDS V6-2 Type 160 – Other Delivery Event 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.

There is also further information 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 for providers across several datasets including HES. 

The UK Statistics Authority conducted case studies of quality assurance and audit arrangements of administrative data sources. HES was used as a case study and further information can be found in the published report (Annex C, case study 3)

Data completeness

The table below provides a count and percentage of records that have valid data in specific key fields.

  2019-20 2020-21
HES maternity key fields Number of valid/known deliveries/records Percentage of valid/known deliveries/records Number of valid/known deliveries/records Percentage of valid/known deliveries/records
Place of delivery 461,318 78 427.632 58
Person conducting delivery 414,996 70 391,055 49
Anaesthetics used before or during delivery 440,640 74 419,438 56
Method of onset of labour 481,510 81 449,978 64
Method of delivery 580,603 98 548,467 96
Duration of antenatal stay 480,789 81 445,327 64
Duration of postnatal stay 480,423 81 444,988 64
Gestation length 456,900 77 418,589 56
Gestation period in weeks at first antenatal assessment date 379,701 64 355,604 41
Birth status 482,780 82 447,533 64
Birth weight 495,839 84 454,053 66
Total deliveries 591,759 n/a 559,728 n/a
Data quality notes

Information about completeness of key data items relevant to this report for each data set is included in the data completeness section of this report.

Detailed information about data quality of HES data items, and completeness of provider data submissions is available. 

Timeliness and punctuality

HES data is 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 data set and a further month to complete publication production and data investigation.

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

The final annual data includes some additional data cleaning and more up-to-date reference data used with the derivations, compared to Month 13 data

Coherence and comparability

Users can misinterpret HES data as relating to numbers of patients but care should be taken as the standard unit of HES data relates to hospital activity, not individuals.

In the case of A&E data, this is presented as attendances, which may include people attending more than once in the reporting period.

Other comparable 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 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. This was discontinued in 2010.

NHS England also publish other 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.

Comparisons of annual HES data

Care should be taken when comparing annual HES data over time, as improvements in coverage in HES will contribute alongside growth from increased activity through the years.

Extra care should be taken when looking at clinical data, as changes in NHS practices (such as the introduction of new procedures and interventions) can have an effect on changes through time.

Accessibility and clarity

As HES is such a rich source of data it is not possible to publish aggregate tables covering all permutations of possible analysis. Underlying HES data is also made available to facilitate further analysis that is of direct relevance to users. There are no restrictions to accessing the published data.

Trade-offs between quality components

As discussed in the Accuracy and Reliability section, providers have the opportunity to submit data each month, which is centrally assessed for data quality and issues is reported back to providers in order to give an opportunity to address any issues found. The dataset is then finalised for the full financial year, and issues remaining after that point are published on NHS Digital’s website, but no attempt is made to amend the data.

Assessment of user needs and perceptions

Users of the data and this publication are encouraged to report and feedback their views and suggestions. We have a dedicated e-mail address for users to e-mail their queries or concerns and if anything is identified as being unclear, we address that as soon as we possibly can. We consult users when proposing significant changes to the content of or methodologies used in the publications.

Cost, performance and respondent burden

The production of HES data is a secondary use of data collected during the care of patients in the NHS and submitted for NHS Providers to be paid for the care they deliver. Therefore HES does not incur additional costs or burden on the providers of the data.

Confidentiality, transparency and security

Although certain information is considered especially sensitive, all information about someone's health and the care they are given must be treated confidentially and in accordance with legislation and NHS Digital protocols at all times.

There are a limited number of people authorised to have access to the record level data, all of whom must adhere to the written protocol issued by NHS Digital on the dissemination of HES data. For example, guidance is given on handling the very small numbers that sometimes occur in tables to reduce the risk that local knowledge could enable the identification of either a patient or clinician.

HES is a record level data warehouse and it contains information that could (if it was made freely available) potentially identify patients or the consultant teams treating them. In some cases, record level data may be provided for medical / health care research purposes. For example, data is likely to be required by the Care Quality Commission and other such bodies. The information may be given following a stringent application procedure, where the project can justify the need and where aggregated data will not suffice. Any request involving sensitive information, or where there may be potential for identification of an individual, is referred to the appropriate governance committee. NHS Digital publishes a quarterly register of data releases, which includes releases of HES data.

HES data is stored to strict standards: a system level security protocol is in place. This details the security standards that are in place to ensure data is secure and only accessed by authorised users.

Last edited: 15 September 2023 5:20 pm