Introduction#

As explained in the UK LLC sample guide, the number of Longitudinal Population Study (LPS) participants in the UK LLC Trusted Research Environment (TRE) changes over time. UK LLC manages this complexity by establishing a ‘data freeze’ of the pooled sample on a quarterly basis. Each freeze comprises a number of tables that summarise the basic characteristics of the UK LLC sample at that point in time, for example, how many participants from each LPS are included in the UK LLC TRE and how many are linked to each of the linked data sources. You can access each individual freeze under the UK LLC sample heading.

Periodically, UK LLC produces a summary of the demographic characteristics of LPS participants in the UK LLC TRE, including their sex, gender, year of birth (as a proxy for age) and ethnic group. This information is drawn from two sources:

• Harmonised LPS demographic variables created by UK LLC [link to harmonised landing page TBC]

• Demographic information provided by NHS England (NHSE) [link to CORE datasets page TBC]

Notes

• The ‘best measure’ in the tables below was determined using a hierarchical approach for each LPS participant. If available, the most recent self-reported data (i.e. LPS data) was selected. Where LPS data was unavailable, NHS England data was used for those participants with linked NHS England records.

• For clarity, all missing data has been grouped into a single category.

UK LLC profile (based on Freeze 11, February 2025)#

All LPS collected sex assigned at birth.
For NHS England, sex was determined using the most recent record from the Personal Demographics Service.

Five LPS collected information about participants’ gender.
NHS England does not provide any gender identification measures.

Ethnicity was collected by most LPS, but to varying degrees of granularity. UK LLC has harmonised LPS data on ethnicity into six, five and two categories to include all LPS that collected these data. Only the most and least granular categories are presented here.

For NHS England, a hierarchy of source reliability established by the British Heart Foundation Data Science Centre was used (https://www.bmj.com/content/373/bmj.n826). Where multiple entries existed from the preferred source, the most recent was given precedence.