Validation of ethnicity in administrative hospital data in women giving birth in England: cohort study

Objective To describe the accuracy of coding ethnicity in National Health Service (NHS) administrative hospital records compared with self-declared maternity booking systems, and to assess potential impact misclassification bias. Design Secondary analysis data from women giving birth England (2015–2017). Setting NHS Trusts participating a national audit programme. Participants 1 237 213 who gave between April 2015 31 March 2017. Primary secondary outcome measures (1) Proportion complete ethnicity; (2) agreement on coded (maternity information systems (MIS)) (Hospital Episode Statistics (HES)) records; (3) rates caesarean section obstetric anal sphincter injury by ethnic group MIS HES. Results 91.3% had regarding Overall sets was 90.4% (?=0.83); 94.4% when collapsed into aggregate groups white/South Asian/black/mixed/other (?=0.86). Most disagreement seen as mixed either set. Rates obstetrical events complications were similar regardless set used, most differences mixed. Conclusions Levels support use (white/South Asian/black/mixed/other), but findings for other groups, more granular classifications, should be treated caution. Robustness results analyses associations can improved using additional primary sources.