title: Predictors of treatment with dialysis modalities in observational studies for comparative effectiveness research.
abstract: BACKGROUND
  The Institute of Medicine has identified the comparative effectiveness of renal replacement therapies as a kidney-related topic among the top 100 national priorities. Given the importance of ensuring internal and external validity, the goal of this study was to identify potential sources of bias in observational studies that compare outcomes with different dialysis modalities.
  
  
  METHODS
  This observational cohort study used data from the electronic medical records of all patients that started maintenance dialysis in the calendar years 2007-2011 and underwent treatment for at least 60 days in any of the 2217 facilities operated by DaVita Inc. Each patient was assigned one of six dialysis modalities for each 91-day period from the date of first dialysis (thrice weekly in-center hemodialysis (HD), peritoneal dialysis (PD), less-frequent HD, home HD, frequent HD and nocturnal in-center HD).
  
  
  RESULTS
  Of the 162 644 patients, 18% underwent treatment with a modality other than HD for at least one 91-day period. Except for PD, patients started treatment with alternative modalities after variable lengths of treatment with HD; the time until a change in modality was shortest for less-frequent HD (median time = 6 months) and longest for frequent HD (median time = 15 months). Between 30 and 78% of patients transferred to another dialysis facility prior to change in modality. Finally, there were significant differences in baseline and time-varying clinical characteristics associated with dialysis modality.
  
  
  CONCLUSIONS
  This analysis identified numerous potential sources of bias in studies of the comparative effectiveness of dialysis modalities.
authors.affiliation: Kidney Research Institute, Division of Nephrology, University of Washington, Seattle, WA, USA.
authors.forename: Sooraj
authors.initials: S
authors.lastname: Kuttykrishnan
authors.affiliation: University of California Irvine, Irvine, CA, USA.
authors.forename: Kamyar
authors.initials: K
authors.lastname: Kalantar-Zadeh
authors.affiliation: Department of Epidemiology, UCLA Fielding School of Public Health, Los Angeles, CA, USA.
authors.forename: Onyebuchi A
authors.initials: OA
authors.lastname: Arah
authors.affiliation: Division of Nephrology & Hypertension, University of Utah, Salt Lake City, UT, USA.
authors.forename: Alfred K
authors.initials: AK
authors.lastname: Cheung
authors.affiliation: DaVita Inc., El Segundo, CA, USA Division of Nephrology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Steve
authors.initials: S
authors.lastname: Brunelli
authors.affiliation: School of Public Health, University of Washington, Seattle, WA, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Heagerty
authors.affiliation: Kidney Research Institute, Division of Nephrology, University of Washington, Seattle, WA, USA.
authors.forename: Ronit
authors.initials: R
authors.lastname: Katz
authors.affiliation: Division of Nephrology, University of Tennessee Health Sciences Center, Memphis, TN, USA.
authors.forename: Miklos Z
authors.initials: MZ
authors.lastname: Molnar
authors.affiliation: DaVita Inc., El Segundo, CA, USA Division of Nephrology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, CA, USA.
authors.forename: Allen
authors.initials: A
authors.lastname: Nissenson
authors.affiliation: University of California Irvine, Irvine, CA, USA.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Ravel
authors.affiliation: University of California Irvine, Irvine, CA, USA.
authors.forename: Elani
authors.initials: E
authors.lastname: Streja
authors.affiliation: Kidney Research Institute, Division of Nephrology, University of Washington, Seattle, WA, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Himmelfarb
authors.affiliation: University of California Irvine, Irvine, CA, USA.
authors.forename: Rajnish
authors.initials: R
authors.lastname: Mehrotra
mesh_terms: D000328:Adult; D015331:Cohort Studies; D057186:Comparative Effectiveness Research; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000517:prevention & control / Q000628:therapy*; D008297:Male; D011379:Prognosis; D006435:Renal Dialysis / Q000145:classification* / Q000706:statistics & numerical data*; D014481:United States
keywords: bias; comparative effectiveness research; end-stage renal disease; hemodialysis; peritoneal dialysis