title: Linking primary and secondary healthcare databases in New Zealand.
abstract: OBJECTIVE
  To investigate the effectiveness of linking primary and secondary care data using an encrypted national health index (ENHI).
  
  
  METHODS
  Primary care patient registers from 106 practices collected by the Dunedin Research Unit of the Royal New Zealand College of General Practitioners (RNZCGP) for the year 2001 were linked to the entire National Minimum Data Set (NMDS) for 2001 using an ENHI. The success of matching using the ENHI was measured, and primary and secondary care populations were compared in terms of hospital utilisation (number of discharges, length of stay, major diagnostic category [MDC]).
  
  
  RESULTS
  86,608 unique general practice ENHIs were successfully linked to the NMDS for the study period. Date of birth was matched on ENHIs (96.6%), sex (99.1%), and ethnicity (84.0%). Hospital morbidity and hospital utilisation (in terms of number of discharges and length of stay) were similar for general practice patient admissions and the entire NMDS admission data set.
  
  
  CONCLUSIONS
  Data collected in general practice linked well to secondary care data using the ENHI. Linked primary and secondary care data sets will provide a sound basis for research into publicly funded healthcare.
authors.affiliation: RNZCGP Research Unit, Department of General Practice, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand. atomlin@gp.otago.ac.nz
authors.forename: Andrew
authors.initials: A
authors.lastname: Tomlin
authors.forename: Jason
authors.initials: J
authors.lastname: Hall
mesh_terms: D019992:Databases as Topic / Q000458:organization & administration*; D003695:Delivery of Health Care / Q000191:economics / Q000458:organization & administration / Q000706:statistics & numerical data*; D005194:Family Practice / Q000458:organization & administration / Q000706:statistics & numerical data; D005380:Financing, Government / Q000706:statistics & numerical data; D006296:Health Services / Q000706:statistics & numerical data; D006302:Health Services Research / Q000379:methods / Q000458:organization & administration / Q000706:statistics & numerical data; D006801:Humans; D008498:Medical Record Linkage / Q000379:methods*; D009520:New Zealand; D010355:Patient Identification Systems / Q000379:methods / Q000706:statistics & numerical data; D011320:Primary Health Care / Q000191:economics / Q000458:organization & administration / Q000706:statistics & numerical data*