I am using the cochrane handbook for assessmen of risk of bias in RCTs
Allocation concealment
• It is defined as ‘the procedure for protecting the randomization process so that the treatment to be allocated is not known before the patient is entered into the study’
Some standard methods of ensuring allocation concealment include
• Sequentially numbered, opaque, sealed envelopes (SNOSE)
• Sequentially numbered containers
• Pharmacy controlled randomization
• Central randomization/ distant randomization
• Distance randomization means that assignment sequence should be completely removed from those who make the assignments
• The investigator, on recruiting a patient, telephones a central randomization service which issues the treatment allocation
Blinding
• The term blinding (sometimes called masking) refers to the practice of preventing study participants, health care professionals, and those collecting and analysing data from knowing who is in the experimental group and who is in the control group, in order to avoid them being influenced by such knowledge
• Single blind
• Double Blind
• Triple Blind
Great question and answers. Another simple but important distinction is how the 3 specific steps of an RCT are designed to control the "big three" biases. So:
Randomization prevents confounding (makes the baseline prognostic factors equal across groups).
Allocation concealment prevents section bias (prevents manipulation of the randomization scheme so the similarity across groups provided by randomization is preserved)
Blinding prevents measurement bias (a.k.a. performance bias) - this occurs post randomization and as well described is not always possible.
Wow. I must say I am learning a lot from the simple yet profound ways in which you have all explained the differences between these concepts. I appreciate the time you have all taken to educate me. Thank you Martín Cañón, Harish M Tharayil, and Mathew J Reeves