Clinical trial design

Controlled trials Back to top

In most trials, one group of patients will have the trial treatment and one group will have the standard treatment. The people having the trial treatment are called the trial group and the people having the standard treatment are the control group. The control group is needed to compare with the treatment group. The results of both groups are compared to tell if there is any benefit from the new treatment, to see if the side effects are better, worse or different, and to measure how much of the improvement in the patients is due to the new treatment and how much would have happened by chance or is due to standard treatment.

Sometimes standard treatment is to ‘watch and wait’. This means that no treatment is given unless the cancer starts to develop or cause symptoms.

Placebo Back to top

Randomisation Back to top

Most phase 3| and some phase 2| trials are randomised. In a randomised trial, a computer selects patients into the treatment groups. This means that if you agree to take part you won’t be able to choose which treatment you are given.

Trials are often randomised because if the researchers or doctors were to decide who should get which treatment, they might be influenced by what they know about their patients. They might put people who they thought were more or less likely to respond to a new treatment into a particular group. This would introduce bias, making the results unreliable.

Bias can be prevented if people are allocated to the treatment groups by a computer. The computer can match the groups so that they are similar – for example, they can be matched so that each group has a similar mix of patients of different ages, sex or state of health. By using matched groups, if one group does better than another group, it’s likely to be because of the treatment, as the two groups are similar.

Blind and double-blind trials Back to top

If you take part in a trial of a new drug you may not be told which treatment group you are in. This is called a blind trial. The medicine used will look the same whether it’s the new treatment, standard treatment or a placebo.

Some randomised trials are called double-blind trials, which means that neither you, nor the doctor treating you, know which treatment you are getting. Your doctor opens a specially coded treatment pack and only the trial organisers know which drug it contains. If necessary, your doctor can find out from the trial coordinators which treatment you’re having, or the pharmacy department at the hospital will be able to break the code.

A blind or double-blind trial aims to reduce any bias. For example, knowing you were having a new treatment might make you feel more positive – or more negative – and influence what you report to the researchers. Similarly, if the researchers knew that you were having a new treatment for which they had high hopes, this might affect how they judged your response to it.