Anonymous linkage of New Zealand mortality and Census data

Aust N Z J Public Health. 2000 Feb;24(1):92-5. doi: 10.1111/j.1467-842x.2000.tb00732.x.


Background: The New Zealand Census-Mortality Study (NZCMS) aims to investigate socio-economic mortality gradients in New Zealand, by anonymously linking Census and mortality records.

Objectives: To describe the record linkage method, and to estimate the magnitude of bias in that linkage by demographic and socio-economic factors.

Methods: Anonymous 1991 Census records, and mortality records for decedents aged 0-74 years on Census night and dying in the three-year period 1991-94, were probabilistically linked using Automatch. Bias in the record linkage was determined by comparing the demographic and socio-economic profile of linked mortality records to unlinked mortality records.

Results: 31,635 of 41,310 (76.6%) mortality records were linked to one of 3,373,896 Census records. The percentage of mortality records linked to a Census record was lowest for 20-24 year old decedents (49.0%) and highest for 65-69 year old decedents (81.0%). By ethnic group, 63.4%, 57.7%, and 78.6% of Maori, Pacific, and decedents of other ethnic groups, respectively, were linked. Controlling for demographic factors, decedents from the most deprived decile of small areas were 8% less likely to be linked than decedents from the least deprived decile, and male decedents from the lowest occupational class were 6% less likely to be linked than decedents from the highest occupational class.

Conclusion: The proportion and accuracy of mortality records linked was satisfactorily high. Future estimates of the relative risk of mortality by socio-economic status will be modestly under-estimated by 5-10%.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Age Distribution
  • Aged
  • Bias
  • Cause of Death
  • Censuses*
  • Child
  • Child, Preschool
  • Confidentiality*
  • Death Certificates*
  • Female
  • Humans
  • Infant
  • Infant, Newborn
  • Linear Models
  • Male
  • Medical Record Linkage / methods*
  • Middle Aged
  • Mortality*
  • New Zealand / epidemiology
  • Population Surveillance / methods*
  • Reproducibility of Results
  • Risk Factors
  • Sex Distribution
  • Socioeconomic Factors*