Blinding
An important part of trial design is deciding on the level of blinding. Generally it is preferable to use the highest level of blinding possible within the trial constraints.
Where blinding isn't possible it is important to have an objective outcome measure that can't be easily influenced by the observer. Alternatively it may be possible to use observers not involved in the patients' care who assess patient outcome without knowing the treatment group.
Levels of blinding
None / unblinded
Blinding is not possible or practical for many trials such as those testing medical devices or involving surgery. Trials of complex interventions such as health care policies or staff training methods are also not easily blinded.
Single blind
This usually refers to the patient being blinded to the treatment given but not the administering clinician. Trials of medical devices or policy in intensive care are usually of this nature because the patient is not fully conscious. Sometimes surgical trials can be single blinded if two different types of surgery are being compared or even if surgery is compared to no surgery (by making a placebo incision in the control group for instance).
Double blind
Neither the patient nor clinician know which treatment the patient is randomised to. Placebo controlled drug trials are usually double blind. It may sometimes be possible for the clinician to guess which treatment the patient has received by blood markers or other side effects. If this is the case the simple randomisation code (see below) is not recommended because the clinician may break the blind on all patients by deducing the simple coding system from one patient.
Type of randomisation code
| Type of code | Description | Example |
|---|---|---|
| Explicit | The name of the treatment itself | surgery/no surgery |
| Simple | A code word for the treatment. Rarely used for double blind trials because breaking the code for one patient unblinds the entire trial. | A/B |
| Unique code | A unique number or code that is linked via a randomisation list to the treatment | 1305 |
Pharmacy based trials
Double blind drug trials are often co-ordinated by the hospital pharmacy at each trial centre. One of the pharmacists will have responsibility for dispensing the trial drug to a patient based on the unique randomisation code for that patient. We provide the pharmacist with a randomisation list for their centre that links up to the randomisation codes on our website or telephone system.