title: Comparison groups in yoga research: a systematic review and critical evaluation of the literature.
abstract: OBJECTIVE
  Comparison groups are essential for accurate testing and interpretation of yoga intervention trials. However, selecting proper comparison groups is difficult because yoga comprises a very heterogeneous set of practices and its mechanisms of effect have not been conclusively established.
  
  
  METHODS
  We conducted a systematic review of the control and comparison groups used in published randomized controlled trials (RCTs) of yoga.
  
  
  RESULTS
  We located 128 RCTs that met our inclusion criteria; of these, 65 included only a passive control and 63 included at least one active comparison group. Primary comparison groups were physical exercise (43%), relaxation/meditation (20%), and education (16%). Studies rarely provided a strong rationale for choice of comparison. Considering year of publication, the use of active controls in yoga research appears to be slowly increasing over time.
  
  
  CONCLUSIONS
  Given that yoga has been established as a potentially powerful intervention, future research should use active control groups. Further, care is needed to select comparison conditions that help to isolate the specific mechanisms of yoga's effects.
authors.affiliation: Department of Psychology, University of Connecticut Storrs, CT, United States. Electronic address: Crystal.park@uconn.edu.
authors.forename: Crystal L
authors.initials: CL
authors.lastname: Park
authors.affiliation: Veterans Affairs San Diego Healthcare System, San Diego, CA, United States; The Health Services Research Center, University of California San Diego, La Jolla, CA, United States.
authors.forename: Erik
authors.initials: E
authors.lastname: Groessl
authors.affiliation: Health Services Research Center, University of California San Diego, La Jolla, CA, United States.
authors.forename: Meghan
authors.initials: M
authors.lastname: Maiya
authors.affiliation: Health Services Research Center, University of California San Diego, La Jolla, CA, United States.
authors.forename: Andrew
authors.initials: A
authors.lastname: Sarkin
authors.affiliation: Center for Healthcare Organization and Implementation Research, Edith Nourse Rogers Memorial Veterans Hospital, Bedford MA United States; Department of Health Policy and Management, Boston University School of Public Health, Boston, MA, United States.
authors.forename: Susan V
authors.initials: SV
authors.lastname: Eisen
authors.affiliation: Department of Psychology, University of Connecticut Storrs, CT, United States.
authors.forename: Kristen
authors.initials: K
authors.lastname: Riley
authors.affiliation: Center for Healthcare Organization and Implementation Research, Edith Nourse Rogers Memorial Veterans Hospital, Bedford MA United States; Department of Health Policy and Management, Boston University School of Public Health, Boston, MA, United States.
authors.forename: A Rani
authors.initials: AR
authors.lastname: Elwy
mesh_terms: D006801:Humans; D016032:Randomized Controlled Trials as Topic; D012107:Research Design; D015013:Yoga
keywords: Comparison group; Control group; Randomized controlled trials; Systematic review; Yoga