The most common terms are included here. If you hear other phrases which you don’t understand, please ask your researcher to explain them.
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.
Treatment will only be chosen in this way if there is no evidence that one is clearly better than the other.
In a blind trial, the patient doesn’t know whether they are receiving the new treatment or standard treatment. This is to avoid influencing how the patient reports back to the researcher. The treatment that all the people in the trial are given will look the same whether it is the new treatment, standard treatment or a placebo.
A double-blind trial means that neither the patient nor the hospital staff will know which treatment is being given. 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.
A placebo is an inactive substance, such as chalk, salt or sugar. It is made into a tablet or injection identical in size, shape and colour to a specific treatment. The patient won’t know whether they are receiving the treatment or placebo. A placebo-controlled trial may also be double-blind.
A proportion of patients will feel better even though their illness isn’t directly affected by the treatment they are given – the 'placebo effect'. It is thought that this happens because we believe a new tablet or injection must be better, even though there has been no change in our health. This effect must be separated from that of the actual treatment, which should give better results than the placebo. If the treatment doesn’t work, the results will be similar to the placebo.
Placebo-controlled trials will be clearly identified to you before your participation.