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Block Randomization with Random Block Sizes

The following code illustrates how to generate the randomization treatment assignments for a randomized clinical trial assuming block randomization with random block sizes.
  • The example code highlighted below is taken from [http://biostat.mc.vanderbilt.edu/SexamplesMisc][this site]].
  • Also check out the blockrand R add-on package.
# Example: --> for two treatments b <- 20 # number of blocks s <- c(2,4) # number of subjects per block set.seed(1) # so can reproduce results m <- sample(s, b, replace=T) # actual number of subjects over blocks # Get treatment assignments for each block, randomized within blocks treats <- vector('list', b) for(i in 1:b) treatsi <- sample(c(rep('a',m[i]/2),rep('b',m[i]/2))) treats # print for statistician use unlist(treats) # print blinded to block boundaries

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# Second example: # --> generate lists for 6 sites # --> N = 100 per site # --> 3 treatment arms (A, B, C) # --> blocks of size 3 and 6 # * Generate a list that is at least 600 elements long * b <- 136 # number of blocks s <- c(3,6) # number of subjects per block set.seed(1) # so can reproduce results m <- sample(s, b, replace=T) # actual number of subjects over blocks # Get treatment assignments for each block, randomized within blocks # --> i.e. randomized permuted block list treats <- vector('list', b) for(i in 1:b) treatsi <- sample(c(rep('A',m[i]/3), rep('B',m[i]/3), rep('C', m[i]/3))) treats # print for statistician use unlist(treats) # print blinded to block boundaries # Check the length of treats --- Need 600 total elements length(unlist(treats)) # Check the randomization using table: table(unlist(treats))

# NOTE: the above lists is 603 elements long, but we only need the # first 600 elements # NOTE: the treatments are no longer equally distributed # among the 600 patients table(unlist(treats)[1:600]) # Create list as dataframe x<-data.frame(id=1:600, treatment=unlist(treats)[1:600]) write.table(x, "randlists.csv", sep=",", row.names=FALSE, quote=FALSE)
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Topic revision: r2 - 09 Nov 2006, TheresaScott
 

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