UK LLC sample

UK LLC sample#

Last modified: 19 Oct 2026

An explanation of the UK LLC sample and the data freeze concept.

The UK LLC sample is the participants whose data are held in the UK LLC TRE. The UK LLC sample is complex and dynamic because:

  • Each Longitudinal Population Study (LPS) provides information to UK LLC on a sub-set of their participants.

  • The sample provided by each LPS will change as new participants join or some withdraw consent to be included in different linkages and/or the UK LLC as a whole.

  • New LPS may join UK LLC and some LPS may withdraw from UK LLC.

Understanding the UK LLC ‘data freeze’ concept#

  • Changes to the UK LLC sample occur in a controlled manner every quarter when LPS are required to communicate to UK LLC any changes to their LPS sample

  • Following updates to the UK LLC sample, UK LLC establishes a ‘data freeze’ which comprises a number of tables that summarise the broad characteristics of the UK LLC sample at that point in time

  • Data freezes are critical in helping researchers to understand the UK LLC sample that underpins the datasets at the point in time they are granted access to them

  • Each data freeze is given a Digital Object Identifier (DOI) and all data tables are retained to help track changes to the UK LLC sample and to promote reproducibility of analyses.

Please visit the individual Freeze pages to understand the current UK LLC sample and to see how the sample has changed over time.

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