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Hi. I'm Olga Kuznetsova.
I'm a Senior Principal Scientist
at Merck & Company.
I will talk about
randomization in studies
with unequal allocation.
0:13
This presentation is largely
based on our joint works
with Dr. Yevgen Tymofyeyev.
0:20
Unequal allocation
where the treatment groups
are planned to have unequal sizes
is often used in clinical trials.
Among common reason
unequal allocation
are power considerations,
better enrollment in a trail
with higher allocation
to the experimental group.
Increased exposure
to the experimental treatment
or reduced cost.
Unequal allocation is often used
in adaptive design studies list
two or more treatment times.
Dose-ranging
or multi-stage studies,
studies with treatment
selection design,
sample size re-estimation
or response adaptive randomization.
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Numerous equal allocation procedures
are developed to meet
different design needs.
Robustness with respect
to the accidental bias
due to a time trend,
reduced potential
for selection bias,
balance in important covariates.
This algorithms
are usually symmetric
with respect to the treatment arms.
As a result all patients,
regardless of their place
in the allocation sequence,
are allocated with the same
unconditional allocation ratio.
For example,
in a study with equal allocation
to two treatments,
the patients allocated first,
second, third and so on,
all have probability of ½
to be allocated
to the first treatment.
