Blinding and Allocation Concealment


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


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


  • 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 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.


  • 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


FOAM and web resources

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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