Allocation concealment blindingmasking

4.8.1 Definitions

Randomization alone is not sufficient to guarantee an unbiased trial. Systematic bias may still be introduced ifthe method ofassessment ofoutcome is subjective or in some other way open to interpretation. To address this, consideration should be given to whether aspects of the trial can be 'blinded' or 'masked.' With respect to treatment allocation, there are three levels of blinding possible.

♦ single blind - the patient does not know which treatment they have been allocated,

♦ double blind - neither patient nor doctor/evaluator knows which treatment the patient has been allocated,

♦ triple blind - neither the patient, nor the doctor, nor those reviewing the interim results and deciding on continuation of the trial know which treatment the patient has been allocated.

In addition, even if treatments are not blinded, the assessment of eligibility or response can in some situations be carried out without knowledge (or 'blind') of the treatment allocation, for example by using an independent reviewer.

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