Control group design, contamination and drop-out in exercise oncology trials: a systematic review

PLoS One. 2015 Mar 27;10(3):e0120996. doi: 10.1371/journal.pone.0120996. eCollection 2015.

Abstract

Purpose: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review
  • Systematic Review

MeSH terms

  • Control Groups*
  • Exercise*
  • Humans
  • Neoplasms / rehabilitation*
  • Quality of Life*
  • Randomized Controlled Trials as Topic
  • Research Design / standards*
  • Survivors*

Grants and funding

Funding was provided from The Netherlands Organisation for Health Research and Development (ZonMw, project number: 171002202), the Dutch Cancer Society (KWF Kankerbestrijding. Project number: UU 2009-4473) and Pink Ribbon (project number: 2011.WO02.C100). The contribution of A.M. May was supported by a ZonMw Veni grant (016.156.050). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.