Misguided precedent is not a reason to use permuted blocks.

Headache The Journal of Head and Face Pain (Impact Factor: 3.19). 07/2006; 46(7):1210-2. DOI: 10.1111/j.1526-4610.2006.00517_2.x
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    ABSTRACT: Large multicenter acute stroke trials demand a randomization procedure with a high level of treatment allocation randomness, an effective control on overall and within-site imbalances, and a minimized time delay of study treatment caused by the randomization procedure. Driven by the randomization algorithm design of A Study of the Efficacy and Safety of Activase (Alteplase) in Patients with Mild Stroke (PRISMS) (NCT02072226), this paper compares operational and statistical properties of different randomization algorithms in local, central, and step-forward randomization settings. Results show that the step-forward randomization with block urn design provides better performances over others. If the concern on the potential time delay is not serious and a central randomization system is available, the minimization method with an imbalance control threshold and a biased coin probability could be a better choice.
    Contemporary Clinical Trials 01/2015; 41. DOI:10.1016/j.cct.2015.01.013
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    ABSTRACT: Stratified permuted block randomization has been the dominant covariate-adaptive randomization procedure in clinical trials for several decades. Its high probability of deterministic assignment and low capacity of covariate balancing have been well recognized. The popularity of this sub-optimal method is largely due to its simplicity in implementation and the lack of better alternatives. Proposed in this paper is a two-stage covariate-adaptive randomization procedure that uses the block urn design or the big stick design in stage one to restrict the treatment imbalance within each covariate stratum, and uses the biased-coin minimization method in stage two to control imbalances in the distribution of additional covariates that are not included in the stratification algorithm. Analytical and simulation results show that the new randomization procedure significantly reduces the probability of deterministic assignments, and improve the covariate balancing capacity when compared to the traditional stratified permuted block randomization. Copyright © 2014 John Wiley & Sons, Ltd.
    Statistics in Medicine 07/2014; 33(30). DOI:10.1002/sim.6266
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    ABSTRACT: Minimization is based on minimizing an imbalance function defined in terms of one or more covariates. Standard (non-adaptive) randomization procedures, on the other hand, generally do not specify or try to minimize an imbalance function. However, it turns out that they may be formulated in this manner. Doing so places adaptive and standard randomization procedures within the same framework, and also suggests novel randomization procedures that combine the best elements of both. Published by Elsevier Inc.
    Contemporary clinical trials 10/2013; 36(2). DOI:10.1016/j.cct.2013.09.017