title: Choosing the net survival method for cancer survival estimation.
abstract: BACKGROUND
  A new net survival method has been introduced by Pohar Perme et al. (2012 [4]) and recommended to substitute the relative survival methods in current use for evaluating population-based cancer survival.
  
  
  METHODS
  The new method is based on the use of continuous follow-up time, and is unbiased only under non-informative censoring of the observed survival. However, the population-based cancer survival is often evaluated based on annually or monthly tabulated follow-up intervals. An empirical investigation based on data from the Finnish Cancer Registry was made into the practical importance of the censoring and the level of data tabulation. A systematic comparison was made against the earlier recommended Ederer II method of relative survival using the two currently available computer programs (Pohar Perme (2013) [10] and Dickman et al. (2013) [11]).
  
  
  RESULTS
  With exact or monthly tabulated data, the Pohar-Perme and the Ederer II methods give, on average, results that are at five years of follow-up less than 0.5% units and at 10 and 14 years 1-2% units apart from each other. The Pohar-Perme net survival estimator is prone to random variation and may result in biased estimates when exact follow-up times are not available or follow-up is incomplete. With annually tabulated follow-up times, estimates can deviate substantially from those based on more accurate observations, if the actuarial approach is not used.
  
  
  CONCLUSIONS
  At 5 years, both the methods perform well. In longer follow-up, the Pohar-Perme estimates should be interpreted with caution using error margins. The actuarial approach should be preferred, if data are annually tabulated.
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Pieni Roobertinkatu 9, FI-00130 Helsinki, Finland; Department of Mathematical Sciences, University of Oulu, Oulu, Finland.
authors.forename: Karri
authors.initials: K
authors.lastname: Seppä
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Pieni Roobertinkatu 9, FI-00130 Helsinki, Finland.
authors.forename: Timo
authors.initials: T
authors.lastname: Hakulinen
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Pieni Roobertinkatu 9, FI-00130 Helsinki, Finland. Electronic address: arun.pokhrel@cancer.fi.
authors.forename: Arun
authors.initials: A
authors.lastname: Pokhrel
mesh_terms: D003110:Colonic Neoplasms / Q000401:mortality; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D005706:Gallbladder Neoplasms / Q000401:mortality; D006801:Humans; D008113:Liver Neoplasms / Q000401:mortality; D008297:Male; D015233:Models, Statistical; D009369:Neoplasms / Q000401:mortality*; D012042:Registries / Q000706:statistics & numerical data*; D016019:Survival Analysis; D013997:Time Factors
keywords: Epidemiologic methods; Models; Neoplasms; Net survival; Prognosis; Relative survival