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Which type of randomization is best for a 2 x 2 crossover design?
(I think block randomization is good)
If my study needs total 26 subjects, how many subjects I want to take
as additional subjects? 26+2 or 26+4?
Is there any special rule for calculating the number of aditional
If I use block randomization, what is the best block size? 2 or 4? why?
In the randomization procedure, Is it necessery to generate separate
randomization codes for total subjects (26) and seperate codes for
additional subjects (2 or 4)? (by using different seed number in SAS
or is it possible to generate one randomization code by using one
seed number for (26+2) or (26+4) subjects?
When we use this addtional subjects in the analysis?
In the case of block randomization, is there any difference in the
result of analysis (90 % C.I and ANOVA table) if I use the following
(1) the blocks are selected randomly and the subjects in each blocks
are also selected randomly. (using the statement block random subject
random in the proc PLAN of SAS pgm)
(2) the blocks are selected orderly and only the subjects in each
block are randomly selected. (using the statement block order subject
random in proc PLAN
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The following message was posted to: PharmPK
1.It is always better to use Block randomisation technique while
Even though it also depends upon how it is described in SOP
(Standard operating procedure).
2.Regarding additional No.of subjects,actually it depends upon
and also upon discretion of sponsor whether he or she wants to take
care of dropouts
and withdrawls in advance,so that standby subjects can be replace.
3.No,there is as such no specific rule for calculating number of
4.In using Block randomisation there is no restriction on block
size,but it is primary
requirment that treatments should be distributed evenly among the
of treatments is done due to take care of repeation of same sequence.
5.No,a common randomisation code is used for generating
randomisation for both the purpose.
6.In case of taking care of dropout and withdrawl subjects.These
are replaced by standby
7.Obviously,there will be no difference in result of analysis (90 %
C.I and ANOVA table)
I think I have cleared your all points.
Nand Kishore Rawat
Ranbaxy Research Labs.
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