Pseudonymisation

Working notes on how to provide access to data to each site whilst minimising exposure to direct identifiers and minimising the risk of re-identification via indirect identifiers.

Technical options considered:

• Keep a single centralised schema and use views to present anonymised identifiers.
• Maintain an anonymised copy of the data (this simplifies the management of permissions but takes more space and may incur in synchronisation errors).
• Provide column- and table-level permissions, hiding identifiable data.

These notes will be built up as per each “bundle”.

OMOP Person bundle

Hide the following items:

• person_source_value : this is very likely to be the local MRN (Medical Record Number).

Replace the following items:

• person_id : in Silver, we will assume that the id is potentially identifying (i.e. it is possible but unlikely that sites chose to use the local hospital number). This value will be replaced by a generated number when transferring data into Gold.

Do not hide the following items (on the basis that these are not direct identifiers):

• Columns relating to the patient’s date of birth.
• Columns relating to gender.

Data Visibility

Data Category	Fields	Description	Bundle	Silver	Gold Pseudo anonymised	Bespoke Release
Episode Descriptor	person_id	ID unique to the data set	OMOP Person	Yes	Yes	Yes
Episode Descriptor	person_source_value	ID unique at the patients site	OMOP Person	Yes	No	No
Direct identifier	NHS number	Only used for Data Linkage	HIC Person	Yes	No	No
Identifying	year_of_birth		OMOP Person	Yes	Yes	Provided as age at admission
Direct identifier	birth_date_time		OMOP Person	Yes	Provided as age at admission	Provided as age at admission
Direct identifier	death_date		HIC Person	Yes	Revert to 01/01/2020 maintaining $\Delta$ with date of admission	Revert to 01/01/2020 maintaining $\Delta$ with date of admission
Identifying	Post Code	Hospital, GP, Person	HIC Person	Yes	Max 2 inbound or transformation to deprivation index	Deprivation Index Only
Date time	visit_start_date	Hospital, ICU, Ward	HIC Person	Yes	Only if directly required by research question	Revert to 01/01/2020 maintaining seasonal cadence
Date time	visit_end_date	Hospital, ICU, Ward	HIC Person	Yes	Only if directly required by research question	Revert to 01/01/2020 maintaining seasonal cadence
Date time	Multiple possibilites	Tests, interventions, results	All Bundles	Yes	Only if directly required by research question	Revert to 01/01/2020 maintaining seasonal cadence
Sensitive	Comorbidities	Sensitive or related diagnosis	Diagnoses	Yes	Only if directly required by research question	No
Sensitive	Diagnosis	Sensitive or related diagnosis	Diagnoses	Yes	Only if directly required by research question	No
Sensitive	Drugs	Sensitive or related diagnosis related	Drugs Basics	Yes	Only if directly required by research question	No
Sensitive	Test Results	Sensitive or related diagnosis related	Pathology Basics	Yes	Only if directly required by research question	No