CICM SAQ 2011.1 Q29

Blinding and allocation concealment are methods used to reduce bias in clinical trials.Blinding: a process by which trial participants and their relatives, care-givers, data collectors and those adjudicating outcomes are unaware of which treatment is being given to the individual participants.

• Prevents clinicians from consciously or subconsciously treating patients differently based on treatment allocation
• Prevents data collectors from introducing bias when there is a subjective assessment to be made for eg “pain score”
• Prevents outcome assessors from introducing bias when there is a subjective outcome assessment to be made for eg Glasgow outcome score.

Traditionally, blinded RCTs have been classified as “single-blind,” “double-blind,” or “triple-blind”; The 2010 CONSORT Statement specifies that authors and editors should not use the terms “single-blind,” “double-blind,” and “triple-blind”; instead, reports of blinded RCT should discuss “If done, who was blinded after assignment to interventions (for example, participants, care providers, those assessing outcomes) and how. Allocation concealment is an important component of the randomization process and refers to the concealment of the allocation of the randomization sequence from both the investigators and the patient. Poor allocation concealment may potential exaggerate treatment effects.

• Methods used for allocation concealment include sealed envelope technique, telephone or web based randomization.
• Allocation concealment effectively ensures that the treatment to be allocated is not known before the patient is entered into the study. Blinding ensures that the patient / physician is blinded to the treatment allocation after enrollment into the study.