Block randomization
blockrand.RdGenerate a randomization list for a single stratum with blocks of varying sizes.
Usage
blockrand(n, arms = LETTERS[seq(2)], blocksizes = 1:4, pascal = TRUE)Details
By default, frequency of the different block sizes is determined using Pascal's triangle. This has the advantage that small and large block sizes are less common than intermediate sized blocks, which helps with making it more difficult to guess future allocations, and reduces the risk of finishing in the middle of a large block.
Unbalanced randomization is possible by specifying the same arm label multiple times.
Examples
set.seed(1)
blockrand(10)
#> seq_in_list block blocksize seq_in_block arm
#> 1 1 1 4 1 A
#> 2 2 1 4 2 B
#> 3 3 1 4 3 B
#> 4 4 1 4 4 A
#> 5 5 2 4 1 A
#> 6 6 2 4 2 B
#> 7 7 2 4 3 A
#> 8 8 2 4 4 B
#> 9 9 3 6 1 B
#> 10 10 3 6 2 B
#> 11 11 3 6 3 A
#> 12 12 3 6 4 B
#> 13 13 3 6 5 A
#> 14 14 3 6 6 A
# different arm labels
blockrand(10, arms = c("Arm 1", "Arm 2"))
#> seq_in_list block blocksize seq_in_block arm
#> 1 1 1 8 1 Arm 1
#> 2 2 1 8 2 Arm 2
#> 3 3 1 8 3 Arm 2
#> 4 4 1 8 4 Arm 2
#> 5 5 1 8 5 Arm 2
#> 6 6 1 8 6 Arm 1
#> 7 7 1 8 7 Arm 1
#> 8 8 1 8 8 Arm 1
#> 9 9 2 2 1 Arm 1
#> 10 10 2 2 2 Arm 2
# block sizes 2, 4, and 6, 2 arms
blockrand(20, blocksizes = 1:3)
#> seq_in_list block blocksize seq_in_block arm
#> 1 1 1 2 1 B
#> 2 2 1 2 2 A
#> 3 3 2 6 1 A
#> 4 4 2 6 2 B
#> 5 5 2 6 3 A
#> 6 6 2 6 4 A
#> 7 7 2 6 5 B
#> 8 8 2 6 6 B
#> 9 9 3 2 1 B
#> 10 10 3 2 2 A
#> 11 11 4 4 1 A
#> 12 12 4 4 2 B
#> 13 13 4 4 3 A
#> 14 14 4 4 4 B
#> 15 15 5 6 1 A
#> 16 16 5 6 2 A
#> 17 17 5 6 3 B
#> 18 18 5 6 4 B
#> 19 19 5 6 5 B
#> 20 20 5 6 6 A
# unbalanced randomisation (2:1)
blockrand(12, arms = c("Arm 1", "Arm 1", "Arm 2"))
#> seq_in_list block blocksize seq_in_block arm
#> 1 1 1 6 1 Arm 2
#> 2 2 1 6 2 Arm 1
#> 3 3 1 6 3 Arm 1
#> 4 4 1 6 4 Arm 1
#> 5 5 1 6 5 Arm 1
#> 6 6 1 6 6 Arm 2
#> 7 7 2 9 1 Arm 2
#> 8 8 2 9 2 Arm 2
#> 9 9 2 9 3 Arm 1
#> 10 10 2 9 4 Arm 1
#> 11 11 2 9 5 Arm 1
#> 12 12 2 9 6 Arm 1
#> 13 13 2 9 7 Arm 2
#> 14 14 2 9 8 Arm 1
#> 15 15 2 9 9 Arm 1
# fixed block sizes
blockrand(10, blocksizes = 2)
#> seq_in_list block blocksize seq_in_block arm
#> 1 1 1 4 1 B
#> 2 2 1 4 2 A
#> 3 3 1 4 3 B
#> 4 4 1 4 4 A
#> 5 5 2 4 1 B
#> 6 6 2 4 2 B
#> 7 7 2 4 3 A
#> 8 8 2 4 4 A
#> 9 9 3 4 1 B
#> 10 10 3 4 2 A
#> 11 11 3 4 3 A
#> 12 12 3 4 4 B