Random allocations in comparative experiments
of known size: balance without blocking
Random allocations in comparative experiments
of known size: balance without blocking
Michael A. Newton , Bret Larget, Rick Chappell, and
R. F. Jacoby.
Technical Report 124, Department of Biostatistics and
Medical Informatics,
University of Wisconsin, Madison.
Issued December 1997.
Abstract:
We consider the problem of randomizing a known number of subjects into
two or more treatment groups when recruitment occurs over an extended
time period, and thus the potential for confounding factors related to
time is a concern. Our proposed design
generates more balanced allocations than
complete randomization, but
can have higher entropy than randomized-block designs.
These conclusions follow a careful analysis of the probability distribution
induced on the allocations. Furthermore,
analysis and simulation indicate that this new design
can exhibit power advantages
over randomized blocking and complete randomization.
Randomization tests have been applied in a series
of cancer chemoprevention trials.
The design may be useful in other experiments where experimental units
are confined to some linear order, such as arrangement in space.
Keywords clinical trials, experimental design,
one-way layout, permutation test, restricted randomization,
relay randomization, urn sampling.
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