Clinical Trials

❘❙❚■ Chapter 7 | RandomizationTable 1. Example of simple randomization.SubjectTreatment1 A2 B3 A4 A5 B6 B7 B8 B9 A10 A11 B12 Btreatments. Therefore, in cases where there are few patients, there is a need forother methods of randomization.Block randomizationThe block randomization method, also known as permuted-block randomization,is a popular method in clinical trials. A block randomization method can be usedto periodically enforce a balance in the number of patients assigned to eachtreatment. The size of each block of allocations must be an integer multiple ofthe number of treatment groups, so with two treatment strategies the block sizecan be either 2, 4, 6, and so on. A block randomization can be implemented inthree steps:Step 1:Step 2:Step 3:Choose the block size and the number of blocks needed to coverthe number of patients in the study.List all possible permutations of treatments in a block.Generate a randomization code for the order in which to select each block.ExampleConsider a clinical trial comparing treatments A and B in 24 patients. Here, weshould choose a block size of 4 because the sequence would become predictablewith blocks of 2, and block sizes of 6 or above are too large for this small samplesize. Using this block size we must ensure that, after every fourth randomized68