Table 1: Availability of personal identifiers in the national pupil database, personal demographic service and hospital episode statistics.

Linkage identifiers	Data sources
	DfE	NHSD
	NPD	PDS	HES
First name(s)	✓	✓
Surname(s)	✓	✓
Date of birth (e.g. 23/02/1988)	✓	✓	✓
Sex	✓	✓	✓
NHS number		✓	✓
Residence postcodes*	✓	✓	✓
Residence postcodes dates**	✓	✓	✓
Anonymised Pupil Matching Reference (aPMR)	✓
UCL HESID			✓

Notes: * Full postcodes (e.g. LS0 0AA) were available in NPD and PDS. For records in NPD a list of postcodes was available over the academic years. For a specific patient’s NHS number in PDS, a list of postcodes was available over time. ** Dates referring to changes is patient’s postcodes over time were available in PDS. Similarly, dates referring to postcodes in academic years were available in NPD. UCL HESID: is a unique and pseudonymised patient-level identifier that can be used to link patient-level information over time and across different modules of the UCL HES extracts. aPMR: anonymised Pupil Matching Reference is a nationally unique and anonymised child-level identifier that can be used to link pupil-level information over time and across different modules of NPD.