title: Comparing Propensity Score Methods for Creating Comparable Cohorts of Chiropractic Users and Nonusers in Older, Multiply Comorbid Medicare Patients With Chronic Low Back Pain.
abstract: OBJECTIVE
  Patients who use complementary and integrative health services like chiropractic manipulative treatment (CMT) often have different characteristics than do patients who do not, and these differences can confound attempts to compare outcomes across treatment groups, particularly in observational studies when selection bias may occur. The purposes of this study were to provide an overview on how propensity scoring methods can be used to address selection bias by balancing treatment groups on key variables and to use Medicare data to compare different methods for doing so.
  
  
  METHODS
  We described 2 propensity score methods (matching and weighting). Then we used Medicare data from 2006 to 2012 on older, multiply comorbid patients who had a chronic low back pain episode to demonstrate the impact of applying methods on the balance of demographics of patients between 2 treatment groups (those who received only CMT and those who received no CMT during their episodes).
  
  
  RESULTS
  Before application of propensity score methods, patients who used only CMT had different characteristics from those who did not. Propensity score matching diminished observed differences across the treatment groups at the expense of reduced sample size. However, propensity score weighting achieved balance in patient characteristics between the groups and allowed us to keep the entire sample.
  
  
  CONCLUSIONS
  Although propensity score matching and weighting have similar effects in terms of balancing covariates, weighting has the advantage of maintaining sample size, preserving external validity, and generalizing more naturally to comparisons of 3 or more treatment groups. Researchers should carefully consider which propensity score method to use, as using different methods can generate different results.
authors.affiliation: Professor, The Geisel School of Medicine at Dartmouth, The Dartmouth Institute for Health Policy and Clinical Practice, Lebanon, NH; Chair, Health Services and Clinical Research Program, Palmer Center for Chiropractic Research, Palmer College of Chiropractic, Davenport, IA. Electronic address: wbw@dartmouth.edu.
authors.forename: William B
authors.initials: WB
authors.lastname: Weeks
authors.affiliation: Professor, The Geisel School of Medicine at Dartmouth, The Dartmouth Institute for Health Policy and Clinical Practice, Davenport, IA.
authors.forename: Tor D
authors.initials: TD
authors.lastname: Tosteson
authors.affiliation: Instructor, The Geisel School of Medicine at Dartmouth, The Dartmouth Institute for Health Policy and Clinical Practice, Lebanon, NH; Director, Health Services Research, Southern California University of Health Sciences, Whittier, CA.
authors.forename: James M
authors.initials: JM
authors.lastname: Whedon
authors.affiliation: Research Fellow, Integrative Health & Wellbeing Research Program, Center for Spirituality & Healing, University of Minnesota, Minneapolis, MN.
authors.forename: Brent
authors.initials: B
authors.lastname: Leininger
authors.affiliation: Associate Professor, The Geisel School of Medicine at Dartmouth, The Dartmouth Institute for Health Policy and Clinical Practice, Lebanon, NH.
authors.forename: Jon D
authors.initials: JD
authors.lastname: Lurie
authors.affiliation: Professor, The Geisel School of Medicine at Dartmouth, The Dartmouth Institute for Health Policy and Clinical Practice, Davenport, IA.
authors.forename: Rand
authors.initials: R
authors.lastname: Swenson
authors.affiliation: Vice Chancellor, Palmer College of Chiropractic, and Director, Palmer Center for Chiropractic Research, Davenport, IA.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Goertz
authors.affiliation: Professor, The Geisel School of Medicine at Dartmouth, Department of Biomedical Data Science, The Dartmouth Institute for Health Policy and Clinical Practice, Lebanon, NH.
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: O'Malley
mesh_terms: D000368:Aged; D059350:Chronic Pain / Q000150:complications / Q000628:therapy*; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000150:complications / Q000628:therapy*; D008297:Male; D026882:Manipulation, Chiropractic; D006278:Medicare; D057216:Propensity Score; D014481:United States
keywords: Chiropractic Manipulation; Medicare; Propensity Score