Randomization assigns experimental units to treatments using a random mechanism, allowing treatment-group differences to be calibrated against the known assignment distribution.
For each new eligible participant, compare the imbalance that would result from each treatment assignment across prespecified baseline covariate margins. Assign with a probability favoring the less imbalanced choice, while retaining a random component and allocation concealment. This targets marginal balance when a large number of joint strata makes stratified randomization with blocks inefficient. It is a sequential allocation rule, and inference should respect its design.
Divide participants into strata defined by prespecified baseline prognostic variables and randomize independently within each stratum. Permuted blocks can keep treatment counts close throughout recruitment. This balances the stratification variable between arms by design, while allocation concealment keeps upcoming assignments hidden. Analyses should account for important design strata where appropriate.
Within each prespecified stratum, choose a block containing fixed equal counts of the two treatment assignments, then randomly permute their order. Every completed block gives exact treatment balance. Variable block sizes and allocation concealment protect against predicting the next assignment. Incomplete final blocks permit a small unavoidable imbalance; odd stratum sizes cannot have exact equal allocation.
Allocation concealment prevents those deciding whether to enroll an eligible participant from knowing the upcoming randomized assignment. It protects the randomized controlled trial against selection based on that assignment. It concerns access to the assignment before enrollment; keeping participants or assessors unaware after assignment is a separate design feature.
Restricted randomization samples assignments from a specified subset preserving features such as block balance, fixed group sizes or allowable treatment sequences. Inference must respect the chosen allocation scheme rather than treating all label permutations as admissible.
Complete randomization chooses uniformly among all treatment assignments having prespecified treatment-arm sizes.
Articles by others on the same topic
Randomization is a process used in research and experiments to assign subjects or experimental units to different groups in a way that is determined entirely by chance. This technique is often utilized to ensure that the results of the study are unbiased and that the groups being compared are as similar as possible in all respects except for the treatment or intervention applied.