title: Death certificate only proportions should be age adjusted in studies comparing cancer survival across populations and over time.
abstract: BACKGROUND
  The proportion of cases notified by death certificate only (DCO) is a commonly used data quality indicator in studies comparing cancer survival across regions and over time. We aimed to assess dependence of DCO proportions on the age structure of cancer patients.
  
  
  METHODS
  Using data from a national cancer survival study in Germany, we determined age specific and overall (crude) DCO proportions for 24 common forms of cancer. We then derived overall (crude) DCO proportions expected in case of shifts of the age distribution of the cancer populations by 5 and 10 years, respectively, assuming age specific DCO proportions to remain constant.
  
  
  RESULTS
  Median DCO proportions across the 24 cancers were 2.4, 3.7, 5.5, 8.5 and 23.9% in age groups 15-44, 45-54, 55-64, 65-74, and 75+, respectively. A decrease of ages by 5 and 10 years resulted in decreases of cancer specific crude DCO proportions ranging from 0.4 to 4.8 and from 0.7 to 8.6 percent units, respectively. Conversely, an increase of ages by 5 and 10 years led to increases of cancer specific crude DCO proportions ranging from 0.8 to 4.8 and from 1.8 to 9.6 percent units, respectively. These changes were of similar magnitude (but in opposite direction) as changes in crude 5-year relative survival resulting from the same shifts in age distribution.
  
  
  CONCLUSIONS
  The age structure of cancer patient populations has a substantial impact on DCO proportions. DCO proportions should therefore be age adjusted in comparative studies on cancer survival across regions and over time.
authors.affiliation: Division of Clinical Epidemiology and Aging Research, German Cancer Research Center (DKFZ), INF 581, 69120 Heidelberg, Germany; Division of Preventive Oncology, National Center for Tumor Diseases (NCT) and German Cancer Research Center (DKFZ), INF 460, 69120 Heidelberg, Germany; German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), INF 280, 69120 Heidelberg, Germany. Electronic address: h.brenner@dkfz.de.
authors.forename: Hermann
authors.initials: H
authors.lastname: Brenner
authors.affiliation: Division of Clinical Epidemiology and Aging Research, German Cancer Research Center (DKFZ), INF 581, 69120 Heidelberg, Germany.
authors.forename: Felipe A
authors.initials: FA
authors.lastname: Castro
authors.affiliation: Cancer Registry of Bremen, Leibniz-Institute for Prevention Research and Epidemiology - BIPS, Achterstraße 30, 28359 Bremen, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Eberle
authors.affiliation: Cancer Registry of Rhineland-Palatinate, Institute for Medical Biostatistics, Epidemiology and Informatics, University Medical Center, Johannes Gutenberg University Mainz, Obere Zahlbacher Straße 69, 55131 Mainz, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Emrich
authors.affiliation: Saarland Cancer Registry, Präsident-Baltz-Straße 5, 66119 Saarbrücken, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Holleczek
authors.affiliation: Institute of Cancer Epidemiology, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Katalinic
authors.affiliation: Division of Clinical Epidemiology and Aging Research, German Cancer Research Center (DKFZ), INF 581, 69120 Heidelberg, Germany.
authors.forename: Lina
authors.initials: L
authors.lastname: Jansen
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D003644:Death Certificates; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000175:diagnosis / Q000401:mortality* / Q000628:therapy; D011379:Prognosis; D012042:Registries / Q000706:statistics & numerical data*; D018570:Risk Assessment; D012307:Risk Factors; D016019:Survival Analysis; D015996:Survival Rate / Q000639:trends*; D013997:Time Factors; D055815:Young Adult
keywords: Age adjustment; Cancer registries; Death certificate only; Methods; Survival