Generate a block-randomized treatment sequence

Generates a randomized treatment assignment sequence for control and treatment arms using a fixed allocation ratio and one or more permitted block sizes.

Usage

randomization(N_total, block = 2, allocation = c(control = 1, treatment = 1))

Arguments

N_total

A required positive integer giving the total number of treatment assignments.

block

A positive integer vector containing one or more permitted block sizes. Every block size must be a multiple of sum(allocation). The default is 2.

allocation

A length-two positive integer vector giving the control to treatment allocation ratio. The default is c(control = 1, treatment = 1). Name the values control and treatment; either supplied order is accepted and matched by name. A legacy unnamed vector remains accepted in c(control, treatment) order. Unequal unnamed values produce a warning because names may be required in a future major release.

Value

An integer treatment assignment vector, coded 0 for control and 1 for treatment.

Details

Complete randomization may not always be ideal due to the chance of drawing a large block assigned to one treatment group, potentially impacting the time to enrollment completion. Therefore, a block randomization allocation may be preferable. The block randomization allocation specification allows for different two-arm randomization ratios, but they must be given in integer form. For every value b in block, the required relationship is b %% sum(allocation) == 0; see the equal- and unequal-allocation examples below.

Examples

# Implementing treatment allocation for control to treatment with 1:1.5
# randomization ratio
randomization(
  N_total = 100,
  block = 5,
  allocation = c(control = 2, treatment = 3)
)
#>   [1] 0 1 1 1 0 1 1 1 0 0 0 1 1 0 1 1 0 0 1 1 1 0 0 1 1 0 1 1 0 1 0 1 1 1 0 0 1
#>  [38] 1 1 0 1 1 0 1 0 0 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 1 1 1 0 1 1 1 0 0 1 1 0 0
#>  [75] 1 0 1 0 1 1 0 0 1 1 1 1 1 1 0 0 1 0 1 1 0 0 1 1 1 0

# Treatment allocation with 2:1 for control to treatment
randomization(
  N_total = 70,
  block = 9,
  allocation = c(treatment = 1, control = 2)
)
#>  [1] 0 1 1 0 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 1 0 1 0 0 0 1 0 1 1 0 0 1 0 0 0 0 0 0
#> [39] 0 1 1 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 0 1 0 0 1 0 1 0 0 1 0 0 0

# Treatment allocation for control to treatment with 1:2 for control
# to treatment with multiple block sizes c(3, 9, 6)
randomization(
  N_total = 100,
  block = c(3, 9, 6),
  allocation = c(control = 1, treatment = 2)
)
#>   [1] 1 0 1 1 1 0 1 1 1 0 0 1 1 0 1 0 1 1 1 1 0 0 1 0 1 0 1 1 1 1 1 0 1 1 0 1 0
#>  [38] 1 1 0 1 1 1 0 1 1 1 0 0 0 1 1 1 1 1 0 1 0 1 1 1 1 0 0 1 1 0 0 1 1 1 1 1 1
#>  [75] 0 0 1 1 1 1 1 0 1 0 0 1 1 1 0 1 0 1 1 0 1 0 0 1 1 1

# For complete randomization set the N_total to block size
randomization(
  N_total = 100,
  block = 100,
  allocation = c(control = 1, treatment = 1)
)
#>   [1] 0 1 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 1 0 0 0 0 0 0 1 0 0 0 1 1 1 1 1 1 0 1
#>  [38] 1 1 0 1 1 0 0 1 1 0 0 1 0 0 1 0 1 0 0 0 0 0 1 1 0 1 1 1 0 0 1 0 1 1 0 1 0
#>  [75] 1 0 0 0 1 0 1 1 0 1 1 0 1 0 0 1 1 1 1 0 1 1 1 0 0 0

# randomization() is a two-arm helper; a multi-arm allocation is rejected.
try(randomization(
  N_total = 60,
  block = 6,
  allocation = c(1, 1, 1)
), silent = TRUE)