Blinding and Allocation Concealment

OVERVIEW

Blinding and allocation concealment are used in Randomised control trials (RCTs) to reduce systematic bias

BLINDING

Blinding is the process by which trial participants and their relatives, care-givers, data collectors and/or those adjudicating outcomes are unaware of which treatment is being given to the individual participants

Benefits

• Prevents clinicians from consciously or subconsciously treating patients differently based on treatment allocation (e.g. detection bias)
• Prevents data collectors from introducing bias when there is a subjective assessment to be made for eg “pain score” (e.g. observer bias)
• Prevents outcome assessors from introducing bias when there is a subjective outcome assessment to be made (e.g. Glasgow outcome Score) (e.g. observer bias)
• Prevents patients from introducing bias when followed up (recall bias)

Description of blinding

• The 2010 CONSORT Statement specifies that authors and editors should not use the terms “single-blind,” “double-blind,” and “triple-blind” as the terms are ambiguous
• 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

Allocation concealment is performed when the treatment allocation system is set up so that the person enrolling participants does not know in advance which treatment the next person will get

• it is necessary for randomisation to be successful in an RCT
• Proper allocation concealment shields knowledge of forthcoming assignments, whereas proper random sequence generation prevents correct anticipation of future assignments based on knowledge of past assignments 
• Methods used for allocation concealment include sealed envelope technique, telephone or web based randomization.

BLINDING VERSUS ALLOCATION CONCEALMENT

• Allocation concealment 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

References and Links

LITFL

• CCC – Randomisation
• CCC – Bias in Research
• CCC – Randomised control trials

FOAM and web resources

• CONSORT Statement — Treatment allocation. What’s so special about randomisation?
• CONSORT Statement — Randomisation: allocation concealment mechanism
• CONSORT Statement — Blinding terminology