title: Empirical study of correlated survival times for recurrent events with proportional hazards margins and the effect of correlation and censoring.
abstract: BACKGROUND
  In longitudinal studies where subjects experience recurrent incidents over a period of time, such as respiratory infections, fever or diarrhea, statistical methods are required to take into account the within-subject correlation.
  
  
  METHODS
  For repeated events data with censored failure, the independent increment (AG), marginal (WLW) and conditional (PWP) models are three multiple failure models that generalize Cox's proportional hazard model. In this paper, we revise the efficiency, accuracy and robustness of all three models under simulated scenarios with varying degrees of within-subject correlation, censoring levels, maximum number of possible recurrences and sample size. We also study the methods performance on a real dataset from a cohort study with bronchial obstruction.
  
  
  RESULTS
  We find substantial differences between methods and there is not an optimal method. AG and PWP seem to be preferable to WLW for low correlation levels but the situation reverts for high correlations.
  
  
  CONCLUSIONS
  All methods are stable in front of censoring, worsen with increasing recurrence levels and share a bias problem which, among other consequences, makes asymptotic normal confidence intervals not fully reliable, although they are well developed theoretically.
authors.affiliation: Universitat de Barcelona, Barcelona, Spain. rvillegas.bios@gmail.com
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Villegas
authors.forename: Olga
authors.initials: O
authors.lastname: Julià
authors.forename: Jordi
authors.initials: J
authors.lastname: Ocaña
mesh_terms: D000402:Airway Obstruction / Q000209:etiology; D000465:Algorithms; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007223:Infant; D015233:Models, Statistical; D009819:Office Visits / Q000706:statistics & numerical data; D052638:Particulate Matter / Q000009:adverse effects; D016016:Proportional Hazards Models; D012008:Recurrence; D012135:Respiratory Sounds / Q000209:etiology; D016019:Survival Analysis; D013997:Time Factors
chemical_list: D052638:Particulate Matter