gsDesign offers the option of using Wang-Tsiatis bounds as an alternative to
the spending function approach to group sequential design.
Wang-Tsiatis bounds include both Pocock and O'Brien-Fleming designs.
Wang-Tsiatis bounds are currently only available for 1-sided and symmetric 2-sided designs.
Wang-Tsiatis bounds are typically used with equally spaced timing between analyses, but
the option is available to use them with unequal spacing.
Wang-Tsiatis bounds are defined as follows. Assume k analyses and let Z_i represent the upper bound and t_i the proportion of the total planned sample size for the i-th analysis, i=1,2,…,k. Let Delta be a real-value. Typically Delta will range from 0 (O'Brien-Fleming design) to 0.5 (Pocock design). The upper boundary is defined by
for i= 1,2,…,k where c depends on the other parameters.
The parameter Delta is supplied to
gsDesign() in the parameter
For O'Brien-Fleming and Pocock designs there is also a calling sequence that does not require a parameter.
The manual is not linked to this help file, but is available in library/gsdesign/doc/gsDesignManual.pdf in the directory where R is installed.
Keaven Anderson keaven\[email protected]
Jennison C and Turnbull BW (2000), Group Sequential Methods with Applications to Clinical Trials. Boca Raton: Chapman and Hall.
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# Pocock design gsDesign(test.type=2, sfu="Pocock") # alternate call to get Pocock design specified using # Wang-Tsiatis option and Delta=0.5 gsDesign(test.type=2, sfu="WT", sfupar=0.5) # this is how this might work with a spending function approach # Hwang-Shih-DeCani spending function with gamma=1 is often used # to approximate Pocock design gsDesign(test.type=2, sfu=sfHSD, sfupar=1) # unequal spacing works, but may not be desirable gsDesign(test.type=2, sfu="Pocock", timing=c(.1, .2)) # spending function approximation to Pocock with unequal spacing # is quite different from this gsDesign(test.type=2, sfu=sfHSD, sfupar=1, timing=c(.1, .2)) # One-sided O'Brien-Fleming design gsDesign(test.type=1, sfu="OF") # alternate call to get O'Brien-Fleming design specified using # Wang-Tsiatis option and Delta=0 gsDesign(test.type=1, sfu="WT", sfupar=0)
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