title: Unlinked vital events in census-based longitudinal studies can bias subsequent analysis.
abstract: OBJECTIVE
  To examine the potential biases arising from the nonlinkage of census records and vital events in longitudinal studies.
  
  
  METHODS
  A total of 56,396 deaths of residents of Northern Ireland in the 4 years after the 2001 Census were linked to the 2001 Census records. The characteristics of matched and nonmatched death records were compared using multivariate logistic regression. Subject attributes were as recorded on the death certificate.
  
  
  RESULTS
  In total, 3,392 (6.0%) deaths could not be linked to a census record. Linkage rates were lowest in young adults, males, the unmarried, people living in communal establishments, or living in areas that were more deprived or had recorded low census enumeration. For those aged less than 65 years at census, this linkage would exclude from analysis 20.2% of suicides and 19.7% of deaths by external causes.
  
  
  CONCLUSIONS
  The nonlinkage of census and death records is a combination of nonenumeration at census and deficient information about the deceased recorded at the time of death. Unmatched individuals may have been more disadvantaged or socially isolated, and analysis based on the linked data set may therefore show some bias and perhaps understate true social gradients.
authors.affiliation: Department of Epidemiology and Public Health, Queen's University, Mulhouse Building, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BJ, Northern Ireland, UK. d.oreilly@qub.ac.uk
authors.forename: Dermot
authors.initials: D
authors.lastname: O'Reilly
authors.forename: Michael
authors.initials: M
authors.lastname: Rosato
authors.forename: Sheelah
authors.initials: S
authors.lastname: Connolly
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015982:Bias; D002423:Cause of Death; D019352:Censuses; D002648:Child; D002675:Child, Preschool; D003644:Death Certificates; D003710:Demography; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D008498:Medical Record Linkage; D008875:Middle Aged; D009660:Northern Ireland; D016017:Odds Ratio; D012959:Socioeconomic Factors