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Randomization in studies with unequal allocation

Published on September 29, 2016   24 min

Other Talks in the Series: The Risk of Bias in Randomized Clinical Trials

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Hi. I'm Olga Kuznetsova. I'm a Senior Principal Scientist at Merck & Company. I will talk about randomization in studies with unequal allocation.
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This presentation is largely based on our joint works with Dr. Yevgen Tymofyeyev.
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Unequal allocation where the treatment groups are planned to have unequal sizes is often used in clinical trials. Among common reason unequal allocation are power considerations, better enrollment in a trail with higher allocation to the experimental group. Increased exposure to the experimental treatment or reduced cost. Unequal allocation is often used in adaptive design studies list two or more treatment times. Dose-ranging or multi-stage studies, studies with treatment selection design, sample size re-estimation or response adaptive randomization.
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Numerous equal allocation procedures are developed to meet different design needs. Robustness with respect to the accidental bias due to a time trend, reduced potential for selection bias, balance in important covariates. This algorithms are usually symmetric with respect to the treatment arms. As a result all patients, regardless of their place in the allocation sequence, are allocated with the same unconditional allocation ratio. For example, in a study with equal allocation to two treatments, the patients allocated first, second, third and so on, all have probability of ½ to be allocated to the first treatment.

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Randomization in studies with unequal allocation

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