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Hospital Episode Statistics linkage to the Mental Health and Learning Disabilities Data Set

Mental Health and Learning Disabilities Data Set (MHLDDS) was previously known as Mental Health Minimum Data Set (MHMDS).

Hospital Episode Statistics (HES) contains around 1 billion records on patients attending Accident and Emergency units, being admitted for treatment or attending outpatient clinics at NHS hospitals in England.

The Mental Health and Learning Disabilities Data Set (MHLDDS) contains data on patient spells of care in NHS-funded adult specialist mental health services, combined with a range of patient-level demographic detail. 

The HES-MHLDDS linkage enables patients' mental health data going back to 2006/07 to be matched to their recorded interactions with acute secondary care services.

The linkage provides the ability to analyse acute patient pathways for mental health service users in England, thereby enabling a much deeper understanding of mental health service users' interactions with acute secondary care. For example, analysis of the data could reveal how many patients in contact with specialist mental health services have been admitted to hospital for self-harm or have attended A&E. This could help users to assess whether mental health service users are receiving appropriate levels of care.

Matching the MHLDDS to HES

The MHLDDS is linked to HES by matching person identifiable data in the MHLDDS person index with patient identifiers in HES (the HES ID index). Matching is performed by comparing patient identifiable fields, such as NHS number, date of birth, gender and/or postcode, which are present in both HES and MHLDDS. For more information see the pdf icon HES-MHLDDS_Data_Matching_Quality_Report [183kb].

The HES-MHLDDS bridging file

The HES-MHLDDS linkage is provided as a bridging file which lists individual HES Identifiers and which MHLDDS Person Identifiers they are linked to, along with the Match Rank and Bridging File Version. The Match Rank indicates at which stage in the linking process the records were matched (see pdf icon Data Matching Quality Report [183kb]). The bridging file version indicates which HES and MHLDDS indexes have been used in the linkage.

Note: The HES Identifiers are pseudonymised so they are specific to each organisation that requests the bridging file. This ensures that the data can be matched to HES extracts the organisation has already received.

The table below demonstrates how data in the bridging file appears.

HES IDMHLDDS Person IDMatch RankBridging File Version




An 'Old_New_HESID' file is also provided. This file lists any HES ID that has changed over time, as shown below. For more Information see the pdf icon HES-MHLDDS_Data_Matching_Quality_Report [183kb].


Accessing the data

Data can only be made available to those who meet the HSCIC's robust Information Governance standards to protect and control how data is managed and, where applicable, an appropriate legal basis is in place. We only provide identifiable data when there is a lawful basis to do so. For more information please visit our applications, approvals and charges page.

The HES-MHLDDS bridging file is available as a standard extract, bespoke extract or for bespoke data linkage to other data sets or third-party data. For further information, please visit the Data Access Request Service page.

To access the bridging file, customers are required to complete an application form, a HES data form and an MHMDS data form. For more information please visit our applications, approvals and charges page.

Data quality

The HES-MHLDDS pdf icon Data Matching Quality Report [183kb] details the linkage matching algorithm and the percentage of MHLDDS records that have been successfully matched to HES. It includes the number of matches identified at each stage of the matching process. The report also includes HES and MHLDDS Validation and Derivation Rules.

When a new statistical publication is released, an associated Data Quality report is produced. The most recent information about HES and MHLDDS Data Quality can be found with the latest publications in the Publications Calendar. This includes a Background Quality Statement about different aspects of data quality and provider-level data quality measures.

Extract timetable

The HES-MHLDDS bridging file is updated on a monthly basis. The bridging file reflects submitted data from both data sets that is three months in arrears, and includes data which may have been updated from a previous month's submission. This means that each bridging file release can update matches identified in previous files. 

Find out more about HES Submission Dates and Mental Health and Learning Disabilities Data Set Submission Dates.

Statistical publications

The HSCIC publishes summary statistics and additional analysis of linked HES-MHLDDS data. These publications demonstrate how the data can be used to show mental health service users' interaction with acute services.

Access HES-MHLDDS publications in the Publications Calendar.

Open data

We release the aggregate data underpinning our statistical publications wherever possible in support of the Government's transparency agenda and to encourage others to make use of the depth of data available.

HES and MHLDDS open data can be accessed via

Find out more about open data.


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