title: Restriction to period of interest improves informative value of death certificate only proportions in period analysis of cancer survival.
abstract: OBJECTIVE
  The proportion of cases registered by death certificates only (DCO) is a widely used indicator for potential bias in cancer survival studies. Period analysis is increasingly used to derive up-to-date cancer survival estimates. We aimed to assess whether reported DCO proportions should be restricted to the specific recent calendar period ("restricted period") or refer to all diagnosis years of included patients ("full period").
  
  
  METHODS
  We assessed correlations of bias in period survival estimates resulting from DCO cases with DCO proportions in the restricted and full period, respectively. We used cancer registry data to simulate bias and DCO proportions resulting from various patterns of underreporting of deceased cases. We show results for six common cancers with very different prognosis and five different age groups.
  
  
  RESULTS
  In all scenarios, the expected bias was highly correlated with expected DCO proportions in both periods, but correlations were consistently higher with DCO proportions in the restricted period.
  
  
  CONCLUSIONS
  In period analyses of cancer survival, DCO proportions for the restricted period of specific interest are a better indicator of potential bias due to underreporting of deceased cases than DCO proportions for all years of diagnosis of included patients.
authors.affiliation: Division of Clinical Epidemiology and Aging Research, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 581, Heidelberg D-69120, Germany; German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg D-69120, 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), Im Neuenheimer Feld 581, Heidelberg D-69120, Germany.
authors.forename: Lina
authors.initials: L
authors.lastname: Jansen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D015982:Bias; D003644:Death Certificates; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000401:mortality*; D015203:Reproducibility of Results; D018426:SEER Program; D013223:Statistics as Topic; D016019:Survival Analysis; D014481:United States; D055815:Young Adult
keywords: Bias; Cancer registries; Death certificate only; Methods; Period analysis; Survival