blockrand {blockrand} | R Documentation |
This function creates random assignments for clinical trials (or any experiment where the subjects come one at a time). The randomization is done within blocks so that the balance between treatments stays close to equal throughout the trial.
blockrand(n, num.levels = 2, levels = LETTERS[seq(length = num.levels)], id.prefix, stratum, block.sizes = 1:4, block.prefix)
n |
The minimum number of subjects to randomize |
num.levels |
The number of treatments or factor levels to randomize between |
levels |
A character vector of labels for the different treatments or factor levels |
id.prefix |
Optional integer or character string to prefix the id column values |
stratum |
Optional character string specifying the stratum being generated |
block.sizes |
Vector of integers specifying the sizes of blocks to use |
block.prefix |
Optional integer or character string to prefix the block.id column |
This function will randomize subjects to the specified treatments
within sequential blocks. The total number of randomizations may end
up being more than n
.
The final block sizes will actually be the product of
num.levels
and block.sizes
(e.g. if there are 2 levels
and the default block sizes are used (1:4) then the actual block sizes
will be randomly chosen from the set (2,4,6,8)).
If id.prefix
is not specified then the id column of the output
will be a sequence of integers from 1 to the number of rows. If
id.prefix
is numeric then this number will be added to the set
of integers. If id.prefix
is a character string then the
numbers will be converted to strings (zero padded) and have the prefix
prepended.
The block.prefix
will be treated in the same way as the
id.prefix
for identifying the blocks. The one difference being
that the block.id
will be converted to a factor in the final
data frame.
For stratified studies the blockrand
function should run once
each for each stratum using the stratum
argument to specify the
current stratum (and using id.prefix
and block.prefix
to
keep the id's unique). The separate data frames can then be combined
using rbind
if desired.
A data frame with the following columns:
id: |
A unique identifier (number or character string) for each row |
stratum: |
Optional, if stratum argument is specfied it
will be replicated in this column |
block.id: |
An identifier for each block of the randomization, this column will be a factor |
block.size |
The size of each block |
treatment |
The treatment assignment for each subject |
Greg Snow greg.snow@intermountainmail.org
plot.blockrand
, sample
, rbind
## stratified by sex, 100 in stratum, 2 treatments male <- blockrand(n=100, id.prefix='M', block.prefix='M',stratum='Male') female <- blockrand(n=100, id.prefix='F', block.prefix='F',stratum='Female') my.study <- rbind(male,female) ## Not run: plot.blockrand(my.study,'mystudy.pdf', top=list(text=c('My Study','Patient: %ID%','Treatment: %TREAT%'), col=c('black','black','red'),font=c(1,1,4)), middle=list(text=c("My Study","Sex: %STRAT%","Patient: %ID%"), col=c('black','blue','green'),font=c(1,2,3)), bottom="Call 123-4567 to report patient entry", cut.marks=TRUE) ## End(Not run)