- Cancer Information
- Cancer treatment
- Clinical trials and research
- Clinical trials explained
- Randomised controlled trials
- Blinded and crossover studies
Blinded and crossover studies
Many randomised controlled trials are blinded studies, which means you won’t know which of the treatments you are receiving. Some trials are run as crossover studies, which means you may have the chance to swap to the other treatment after a time.
In a blinded study, participants don’t know which arm of a study they’re in. Some randomised controlled trials are called double-blind studies as neither the participant nor the research team know who is receiving the experimental or control treatment. In a double-blind trial, the researchers only discover who is in each arm of the study at the end of the trial when the results are being analysed.
Blinding is used only when participants can’t tell the difference between the two types of treatment. It is not used when the control and experimental treatment are noticeably different – for example, it would be hard to hide surgery and massage from the participant.
The aim of blinding is to reduce bias in the reporting of benefits and side effects. If you don’t know which treatment you’re having, the results are less likely to be influenced by your or your doctor’s views. For example, if you or your doctor knew you were having the experimental treatment, you might report that you’re feeling better than you actually are because you believe you are having a more effective treatment. In an emergency, your doctor can find out what treatment you’re having by contacting those running the study.
In crossover studies, the people in each trial arm receive that treatment for a time and may then have the opportunity to swap to the other treatment. This can mean all participants have all treatments and helps confirm which is the most effective. If the new treatment doesn’t work as hoped with the first group, the second group won’t cross over. You also won’t cross over if you are doing well on the first treatment.
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A/Prof Brett Hughes, Senior Staff Specialist, Medical Oncology, Royal Brisbane and Women’s Hospital and The Prince Charles Hospital, and Associate Professor, The University of Queensland, QLD; Christie Allan, Clinical Trials Lead, Cancer Council Victoria, VIC; Dawn Bedwell, 13 11 20 Consultant, Cancer Council Queensland, QLD; Joanne Benhamu, Senior Research Nurse, Team Lead, Lung, Colorectal and Palliative Care Trials, Parkville Cancer Clinical Trials Unit, Peter MacCallum Cancer Centre, VIC; Louise Dillon, Consumer; Sabina Jelinek, Clinical Nurse Research, St John of God Murdoch Hospital, WA; Chloe Jennett, Program Coodinator, Cancer Research, Cancer Council NSW; Carmel McCarthy, Consumer; Alison Richards, Research Unit Manager, Medical Oncology Clinical Trials Unit, Flinders Medical Centre, SA; Prof Jane Ussher, Translational Health Research Institute (THRI), School of Medicine, Western Sydney University, NSW; Prof Janette Vardy, Medical Oncologist, Concord Cancer Centre, and Professor of Cancer Medicine, The University of Sydney, NSW.
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