title: Methodological issues in linking study participants to Australian cancer registries using different methods: lessons from a cohort study.
abstract: OBJECTIVE
  To compare results of concurrent linkage of records from the same occupational cohort to cancer registries at both a State and national level. Methodological issues affecting the record registry linkage process will be explored in cases of discordant results between the State and national cancer linkages.
  
  
  METHODS
  The number of incident invasive cancers in an occupational cohort of more than 11,000 workers was determined by linkage to the National Cancer Statistics Clearing House (NCSCH) in 2003. The results were then compared with linkages by the cancer registries of Victoria and Western Australia in 2004, and also with a previous NCSCH linkage in 1998.
  
  
  RESULTS
  Our analyses show an under-ascertainment of confirmed cancer cases by the NCSCH of about 13% (26/205) in Victoria and 11% (32/297) in Western Australia. In addition, 14 cases (5%) identified in a previous NCSCH record linkage in 1998 were not matched in 2003.
  
  
  CONCLUSIONS
  These findings strongly indicate that record linkage to the State cancer registries was essential to maximise the ascertainment of cancer cases in our cohort. We attribute the discordant linkage results to differences in the quality of the record linkage process by the cancer registries.
  
  
  CONCLUSIONS
  The record linkage methods of the national and State cancer registries need further standardisation. At present it is advisable to perform cancer record linkages through the State registries in addition to or instead of the NCSCH.
authors.affiliation: Department of Epidemiology and Preventive Medicine, Central and Eastern Clinical School, Alfred Hospital, Monash University, Victoria.
authors.forename: Jan Lucas
authors.initials: JL
authors.lastname: Hoving
authors.forename: Anthony
authors.initials: A
authors.lastname: Del Monaco
authors.forename: Ewan
authors.initials: E
authors.lastname: MacFarlane
authors.forename: Lin
authors.initials: L
authors.lastname: Fritschi
authors.forename: Geza
authors.initials: G
authors.lastname: Benke
authors.forename: Dean
authors.initials: D
authors.lastname: McKenzie
authors.forename: Malcolm
authors.initials: M
authors.lastname: Sim
mesh_terms: D001315:Australia / Q000453:epidemiology; D015331:Cohort Studies; D003628:Database Management Systems; D015340:Epidemiologic Research Design; D006801:Humans; D015994:Incidence; D008498:Medical Record Linkage / Q000379:methods* / Q000592:standards; D009369:Neoplasms / Q000453:epidemiology*; D012042:Registries / Q000592:standards / Q000706:statistics & numerical data*; D014739:Victoria / Q000453:epidemiology; D014904:Western Australia / Q000453:epidemiology