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Research and new methods

Randomisation: the fairness of chance

Randomisation means assigning participants to groups by chance, like drawing lots. It makes the comparison fair.

Last updated: ~1 min read
A fork
Figure 1.A fork — Randomisation: the fairness of chance

01Short answer

If the doctor or patient chose the group, stronger patients might, for example, end up on the new treatment and the result would look misleading. Assignment by chance balances age, disease severity and other factors between the groups. A computer program does the assigning; neither doctor nor patient can choose. Sometimes a trial is blinded, meaning the participant or doctor does not know the group; it can be revealed in an emergency. Agreeing to randomisation is the participant's decision.

02Simple explanation

Assigned by chance.

Balanced groups.

No choosing.

Consent is yours.

03Scientific explanation

NCI: randomisation makes the groups similar, so that differences in results are due to the treatment.

NCI: new treatments are tested step by step, from the laboratory to clinical trials; only those proven safe and beneficial become standard care.

04What happens in the body?

Blinding

The participant and/or doctor does not know the group.

Three white envelopes sealed with wax
Figure 2.Sealed envelopes

Bias

A systematic error that distorts results.

Balanced groups
Figure 3.Balanced groups — Randomisation: the fairness of chance

How to read the news

Research news brings hope, but not every advance suits everyone. Look at who it was tested in, at what phase and in how many people.

Talk to your doctor

Show your doctor what you have read; they will explain how it relates to your diagnosis and treatment. Do not change your treatment on your own.

05From research news to a conversation: four steps

Read, check, ask, decide together.

Read — From a trusted source.1ReadFrom a trusted source.
Check — Phase, participants, result.2CheckPhase, participants, result.
Ask — Show your doctor.3AskShow your doctor.
Decide — Together, without rushing.4DecideTogether, without rushing.
SourceA trusted site.
DoctorA personal explanation.
SafetyNot changing treatment yourself.

06Key points at a glance

TopicIn brief
BlindingThe participant and/or doctor does not know the group.
BiasA systematic error that distorts results.
How to read the newsResearch news brings hope, but not every advance suits everyone. Look at who it was tested in, at what phase and in how many people.
Talk to your doctorShow your doctor what you have read; they will explain how it relates to your diagnosis and treatment. Do not change your treatment on your own.

07Key terms

Randomisation
Assignment by chance.
Bias
Systematic distortion.
Clinical trial
Testing a new treatment with volunteers.
Evidence
A result confirmed by reliable research.

08Key points

  • Let chance decide.
  • Balance the groups.
  • Compare fairly.
  • Check the source.
  • Talk to your doctor.

09Frequently asked questions

Can I choose my group?

Not in a randomised trial; that is key to reliable results.

Will I know my group?

In an open trial, yes; in a blinded one, later.

Is this advance right for me?

Only your treating doctor can say, based on your diagnosis, stage and condition.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Can I choose my group?

  2. Will I know my group?

  3. Is this advance right for me?

My questions

12Sources

  1. National Cancer Institute. Randomization in Clinical Trials
  2. National Cancer Institute. NCI Dictionary of Cancer Terms: randomized clinical trial
  3. National Cancer Institute. What Are Clinical Trials?
  4. National Cancer Institute. Phases of Clinical Trials
  5. National Cancer Institute. Using Trusted Resources
  6. Cancer Research UK. Find a clinical trial
  7. Indian Council of Medical Research. Clinical Trials Registry – India
  8. National Cancer Institute. NCI Dictionary of Cancer Terms: in vitro
  9. National Cancer Institute. NCI Dictionary of Cancer Terms: in vivo
  10. National Cancer Institute. NCI Dictionary of Cancer Terms: animal model
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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