title: Control group design, contamination and drop-out in exercise oncology trials: a systematic review.
abstract: OBJECTIVE
  Important considerations for exercise trials in cancer patients are contamination and differential drop-out among the control group members that might jeopardize the internal validity. This systematic review provides an overview of different control groups design characteristics of exercise-oncology trials and explores the association with contamination and drop-out rates.
  
  
  METHODS
  Randomized controlled exercise-oncology trials from two Cochrane reviews were included. Additionally, a computer-aided search using Medline (Pubmed), Embase and CINAHL was conducted after completion date of the Cochrane reviews. Eligible studies were classified according to three control group design characteristics: the exercise instruction given to controls before start of the study (exercise allowed or not); and the intervention the control group was offered during (any (e.g., education sessions or telephone contacts) or none) or after (any (e.g., cross-over or exercise instruction) or none) the intervention period. Contamination (yes or no) and excess drop-out rates (i.e., drop-out rate of the control group minus the drop-out rate exercise group) were described according to the three design characteristics of the control group and according to the combinations of these three characteristics; so we additionally made subgroups based on combinations of type and timing of instructions received.
  
  
  RESULTS
  40 exercise-oncology trials were included based on pre-specified eligibility criteria. The lowest contamination (7.1% of studies) and low drop-out rates (excess drop-out rate -4.7±9.2) were found in control groups offered an intervention after the intervention period. When control groups were offered an intervention both during and after the intervention period, contamination (0%) and excess drop-out rates (-10.0±12.8%) were even lower.
  
  
  CONCLUSIONS
  Control groups receiving an intervention during and after the study intervention period have lower contamination and drop-out rates. The present findings can be considered when designing future exercise-oncology trials.
authors: Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht, the Netherlands.
authors: Charlotte N
authors: CN
authors: Steins Bisschop
authors: Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada.
authors: Kerry S
authors: KS
authors: Courneya
authors: Comprehensive Cancer Center the Netherlands (IKNL), Utrecht, the Netherlands.
authors: Miranda J
authors: MJ
authors: Velthuis
authors: Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht, the Netherlands.
authors: Evelyn M
authors: EM
authors: Monninkhof
authors: Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors: Lee W
authors: LW
authors: Jones
authors: Department of Population Health Research, Cancer Control Alberta, Alberta Health Services, Calgary, Canada; Department of Community Health Sciences, Faculty of Medicine, University of Calgary, Calgary, Canada; Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Canada.
authors: Christine
authors: C
authors: Friedenreich
authors: Cancer Center, University Medical Center Utrecht, Utrecht, the Netherlands.
authors: Elsken
authors: E
authors: van der Wall
authors: Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht, the Netherlands.
authors: Petra H M
authors: PH
authors: Peeters
authors: Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht, the Netherlands.
authors: Anne M
authors: AM
authors: May
mesh_terms: D035061:Control Groups; D015444:Exercise; D006801:Humans; D009369:Neoplasms / Q000534:rehabilitation*; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic; D012107:Research Design / Q000592:standards*; D017741:Survivors