  Randomization is a common technique used in clinical trials to eliminate
potential bias and confounders in a patient population. Equal allocation to
treatment groups is the standard due to its optimal efficiency in many cases.
However, in certain scenarios, unequal allocation can improve efficiency. In
superiority trials with more than two groups, the optimal randomization is not
always a balanced randomization. In non-inferiority trials, additive margin
with equal variance is the only instance with balanced randomization. Optimal
randomization for non-inferiority trials can be far from 1:1 and can greatly
improve efficiency, a fact which is commonly overlooked. A tool for sample size
calculation for non-inferiority trials with additive or multiplicative margin
with normal, binomial or Poisson distribution is available at
http://www.statlab.wisc.edu/shiny/SSNI/.
