Table 1. Summary of proposed data sets.

Data sources	Description of data set
National Neonatal Research Database(NNRD)	Overseen by the Neonatal Data Analysis Unit and contains demographic, clinical and administrative data for all neonates admitted to neonatal units across Great Britain.13 Its population coverage is internationally unique with 100% coverage of England and Wales since 2012 and high representative coverage since 2008.12 It also contains 2-year neurodevelopmental follow-up records for certain high-risk groups of neonates.13 27
Personal Demographic Service (PDS)	Controlled by NHS England, the PDS contains demographic data for all NHS patients in England with an NHS number.
Hospital Episode Statistics (HES)HES admitted patient careHES accident and emergencyHES emergency care data setHES outpatientsHES-ONS linked mortality data	Controlled by NHS England. Contains all data pertaining to NHS-funded hospital admissions, outpatient appointments and emergency department attendances across England.28 It has been extensively used to investigate longitudinal population health outcomes because it is uniquely positioned to do so with its universal coverage and patient-level data.28 29Additionally, ONS mortality records are routinely linked to HES records to provide population data on cause and time of death.
Mental Health Services Data Set	Controlled by NHS England. Contains individual-level data for all children accessing mental healthcare across the community, outpatient and inpatient settings in England from 2016.
National Pupil Database (NPD)School enrolment:NPD school census pupil levelNPD pupil referral unit censusNPD alternative provision censusAttainment:NPD early years foundation stage profileNPD phonicsNPD key stage 1NPD key stage 2Other:NPD absencesNPD exclusions	Controlled by the Department for Education. Contains detailed pupil-level information on characteristics of pupils in state-funded schools, their educational attainment, special educational needs provision and attendance of all children at state schools across England. These data have previously been linked to health data successfully with linkage rates of over 80%.15 30
Social care dataChildren Looked After Return (CLA)Child In Need Census (CIN)	The CLA is a national data set that contains data on all looked-after children in England.31 It is held by the Department for Education and contains individual-level data.The CIN is also a national individual-level data set held by the Department for Education.26 It contains longitudinal data on children deemed to be in need, that is, those who have been referred to the local authority for social care support in England. Referrals accepted by the local authority are included in the CIN. These include children in care, children on child protection plans and disabled children (who are receiving services from the local authority). Looked-after children appear in both the CLA and CIN data sets.

NHSNational Health ServiceONSOffice for National Statistics