title: Estimation of renal allograft half-life: fact or fiction?
abstract: BACKGROUND
  Renal allograft half-life time (t½) is the most straightforward representation of long-term graft survival. Since some statistical models overestimate this parameter, we compare different approaches to evaluate t½.
  
  
  METHODS
  Patients with a 1-year functioning graft transplanted in Spain during 1990, 1994, 1998 and 2002 were included. Exponential, Weibull, gamma, lognormal and log-logistic models censoring the last year of follow-up were evaluated. The goodness of fit of these models was evaluated according to the Cox-Snell residuals and the Akaike's information criterion (AIC) was employed to compare these models.
  
  
  RESULTS
  We included 4842 patients. Real t½ in 1990 was 14.2 years. Median t½ (95% confidence interval) in 1990 and 2002 was 15.8 (14.2-17.5) versus 52.6 (35.6-69.5) according to the exponential model (P < 0.001). No differences between 1990 and 2002 were observed when t½ was estimated with the other models. In 1990 and 2002, t½ was 14.0 (13.1-15.0) versus 18.0 (13.7-22.4) according to Weibull, 15.5 (13.9-17.1) versus 19.1 (15.6-22.6) according to gamma, 14.4 (13.3-15.6) versus 18.3 (14.2-22.3) according to the log-logistic and 15.2 (13.8-16.6) versus 18.8 (15.3-22.3) according to the lognormal models. The AIC confirmed that the exponential model had the lowest goodness of fit, while the other models yielded a similar result.
  
  
  CONCLUSIONS
  The exponential model overestimates t½, especially in cohorts of patients with a short follow-up, while any of the other studied models allow a better estimation even in cohorts with short follow-up.
authors.affiliation: Department of Nephrology, Hospital Universitari Vall d'Hebron, Barcelona, Spain. [corrected]
authors.forename: M Antonieta
authors.initials: MA
authors.lastname: Azancot
authors.forename: Carme
authors.initials: C
authors.lastname: Cantarell
authors.forename: Manel
authors.initials: M
authors.lastname: Perelló
authors.forename: Irina B
authors.initials: IB
authors.lastname: Torres
authors.forename: Daniel
authors.initials: D
authors.lastname: Serón
authors.forename: Daniel
authors.initials: D
authors.lastname: Seron
authors.forename: Francesc
authors.initials: F
authors.lastname: Moreso
authors.forename: Manuel
authors.initials: M
authors.lastname: Arias
authors.forename: Josep M
authors.initials: JM
authors.lastname: Campistol
authors.forename: Jordi
authors.initials: J
authors.lastname: Curto
authors.forename: Domingo
authors.initials: D
authors.lastname: Hernandez
authors.forename: José M
authors.initials: JM
authors.lastname: Morales
authors.forename: Ana
authors.initials: A
authors.lastname: Sanchez-Fructuoso
authors.forename: Victor
authors.initials: V
authors.lastname: Abraira
mesh_terms: D000328:Adult; D005260:Female; D005500:Follow-Up Studies; D006085:Graft Survival; D006207:Half-Life; D006801:Humans; D007676:Kidney Failure, Chronic / Q000401:mortality* / Q000628:therapy*; D016030:Kidney Transplantation / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D011379:Prognosis; D012307:Risk Factors; D015996:Survival Rate; D014184:Transplantation, Homologous