How are clinical trials designed? 

There are many ways of organising clinical trials. The most common terms are included below:

Randomised trials

In a randomised trial, patients may receive either the best available treatment or the new one. To make sure that one treatment isn’t favoured over the other, the treatment each patient receives is decided by a process called randomisation. This means that the treatment is not chosen by the patient or their doctor but by a computer. There is usually a 50/50 chance of receiving either treatment. Equal numbers of patients of similar age, gender etc, will be put into each treatment group. As far as possible, the only difference between the groups is the treatment they receive. Several hundred patients may be needed to show a difference which is greater than that which could occur by chance.

Blinded trials

A blind trial is a type of clinical trial where the patient does not know whether they are having the treatment that is being tested, or a fake inactive treatment (placebo) that appears to be the same.

This is to avoid influencing how the patient reports back to the researcher.

Double blind trials

A trial where neither the doctor nor the patient know which treatment the patient is having. These trials are designed to try to prevent bias affecting the trial results.

A special code is used and this is broken at the end of the trial to analyse the results. The advantage of the code is that it prevents the staff from favouring one treatment or the other when assessing the benefits or side effects.

The code is always available and can be broken to identify the treatment if it is thought to be necessary or in the patient’s best interests. A double-blind trial can only be used when no special precautions or procedures are needed with one or other treatment.


Eligibility means suitability to enter a clinical trial. To be eligible for a trial a person needs to meet the entry criteria (a list of conditions that must be fulfilled) for example, having a particular type of cancer or having particular blood results

Informed consent

Agreeing to take part in a clinical trial, or have a particular treatment, with a full understanding of the benefits and drawbacks.

What is a clinical trial?
The research team
Current (open) clinical trials
Contact the clinical trials team