title: Comparison between parametric and semi-parametric cox models in modeling transition rates of a multi-state model: application in patients with gastric cancer undergoing surgery at the Iran cancer institute.
abstract: BACKGROUND
  Research on cancers with a high rate of mortality such as those occurring in the stomach requires using models which can provide a closer examination of disease processes and provide researchers with more accurate data. Various models have been designed based on this issue and the present study aimed at evaluating such models.
  
  
  METHODS
  Data from 330 patients with gastric cancer undergoing surgery at Iran Cancer Institute from 1995 to 1999 were analyzed. Cox-Snell Residuals and Akaike Information Criterion were used to compare parametric and semi-parametric Cox models in modeling transition rates among different states of a multi-state model. R 2.15.1 software was used for all data analyses.
  
  
  RESULTS
  Analysis of Cox-Snell Residuals and Akaike Information Criterion for all probable transitions among different states revealed that parametric models represented a better fitness. Log-logistic, Gompertz and Log-normal models were good choices for modeling transition rate for relapse hazard (state 1?state 2), death hazard without a relapse (state 1?state 3) and death hazard with a relapse (state 2?state 3), respectively.
  
  
  CONCLUSIONS
  Although the semi-parametric Cox model is often used by most cancer researchers in modeling transition rates of multi- state models, parametric models in similar situations- as they do not need proportional hazards assumption and consider a specific statistical distribution for time to occurrence of next state in case this assumption is not made - are more credible alternatives.
authors.affiliation: Department of Epidemiology and Biostatistics, University of Medical Sciences, Tehran, Iran E-mail : mahmoodim@tums.ac.ir.
authors.forename: Ali
authors.initials: A
authors.lastname: Zare
authors.forename: Mahmood
authors.initials: M
authors.lastname: Mahmoodi
authors.forename: Kazem
authors.initials: K
authors.lastname: Mohammad
authors.forename: Hojjat
authors.initials: H
authors.lastname: Zeraati
authors.forename: Mostafa
authors.initials: M
authors.lastname: Hosseini
authors.forename: Kourosh Holakouie
authors.initials: KH
authors.lastname: Naieni
mesh_terms: D002173:Cancer Care Facilities / Q000706:statistics & numerical data*; D006801:Humans; D007492:Iran; D009364:Neoplasm Recurrence, Local / Q000401:mortality / Q000601:surgery*; D011379:Prognosis; D016016:Proportional Hazards Models; D018570:Risk Assessment / Q000379:methods; D013274:Stomach Neoplasms / Q000401:mortality / Q000601:surgery*; D015996:Survival Rate