title: The analysis of longitudinal quality of life measures with informative drop-out: a pattern mixture approach.
abstract: OBJECTIVE
  The analysis of longitudinal health-related quality of life measures (HRQOL) can be seriously hampered due to informative drop-out. Random effects models assume Missing At Random and do not take into account informative drop-out. We therefore aim to correct the bias due to informative drop-out.
  
  
  METHODS
  Analyses of data from a trial comparing standard-dose and high-dose chemotherapy for patients with breast cancer with respect to long-term impact on HRQOL will serve as illustration. The subscale Physical Function (PF) of the SF36 will be used. A pattern mixture approach is proposed to account for informative drop-out. Patterns are defined based on events related to HRQOL, such as death and relapse. The results of this pattern mixture approach are compared to the results of the commonly used random effects model.
  
  
  RESULTS
  The findings of the pattern mixture approach are well interpretable, and different courses over time in different patterns are distinguished. In terms of estimated differences between standard dose and high dose, the results of both approaches are slightly different, but have no consequences for the clinical evaluation of both doses.
  
  
  CONCLUSIONS
  Under the assumption that drop-out is at random within the patterns, the pattern mixture approach adjusts the estimates to a certain degree. This approach accounts in a relatively simple way for informative drop-out.
authors.affiliation: Department of Epidemiology, University Medical Center Groningen, Groningen, The Netherlands. w.j.post@rug.nl
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Post
authors.forename: Ciska
authors.initials: C
authors.lastname: Buijs
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Stolk
authors.forename: Elisabeth G E
authors.initials: EG
authors.lastname: de Vries
authors.forename: Saskia
authors.initials: S
authors.lastname: le Cessie
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000453:epidemiology*; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008137:Longitudinal Studies; D008875:Middle Aged; D015233:Models, Statistical; D009426:Netherlands / Q000453:epidemiology; D010352:Patient Dropouts / Q000706:statistics & numerical data*; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic; D013223:Statistics as Topic / Q000379:methods*; D016019:Survival Analysis
chemical_list: D000970:Antineoplastic Agents