title: Modeling survival of arteriovenous accesses for hemodialysis: semiparametric versus parametric methods.
abstract: OBJECTIVE
  Comparing outcomes of arteriovenous grafts and fistulas is challenging because the pathophysiology of access dysfunction and failure rate profiles differ by access type. Studying how risks vary over time may be important.
  
  
  METHODS
  Longitudinal data from 535 incident hemodialysis patients were used to study the relationship between access type and access survival, without (semiparametric Cox modeling) and with specification of the underlying hazard function (parametric Weibull modeling).
  
  
  RESULTS
  The hazard for failure of fistulas and grafts declined over time, becoming proportional only after 3 months from surgery, with a graft versus fistula hazard ratio of 3.2 (95% confidence interval 1.9 to 5.3; Cox and Weibull estimation) and time ratio of 0.11 (i.e., the estimated access survival time was approximately one tenth shorter in grafts; 95% confidence interval 0.04 to 0.28; Weibull estimation only). Considering the entire observation period, grafts had slower hazard decline (P<0.001) with shorter median survival times than fistulas (8.4 versus 38.3 months; Weibull regression only).
  
  
  CONCLUSIONS
  Parametric models of arteriovenous access survival may provide relevant information about temporal risk profiles and predicted survival times.
authors.affiliation: Department of Medicine, Division of Nephrology, University of Calgary, Foothills Medical Centre, 1403 29th St NW, Calgary, AB, T2N2T9, Canada. pravani@ucalgary.ca
authors.forename: Pietro
authors.initials: P
authors.lastname: Ravani
authors.forename: Patrick
authors.initials: P
authors.lastname: Parfrey
authors.forename: Jennifer
authors.initials: J
authors.lastname: MacRae
authors.forename: Matthew
authors.initials: M
authors.lastname: James
authors.forename: Robert
authors.initials: R
authors.lastname: Quinn
authors.forename: Fabio
authors.initials: F
authors.lastname: Malberti
authors.forename: Giuliano
authors.initials: G
authors.lastname: Brunori
authors.forename: Salvatore
authors.initials: S
authors.lastname: Mandolfo
authors.forename: Marcello
authors.initials: M
authors.lastname: Tonelli
authors.forename: Brenda
authors.initials: B
authors.lastname: Hemmelgarn
authors.forename: Braden
authors.initials: B
authors.lastname: Manns
authors.forename: Brendan
authors.initials: B
authors.lastname: Barrett
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001166:Arteriovenous Shunt, Surgical / Q000009:adverse effects / Q000706:statistics & numerical data; D002170:Canada; D005260:Female; D006085:Graft Survival; D006801:Humans; D007558:Italy; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D016016:Proportional Hazards Models; D006435:Renal Dialysis; D012086:Reoperation; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome