Stipulates alpha spending according to the Wang-Tsiatis
Power function in the Lan-Demets boundary construction method. Its
intended purpose is in constructing calls to
The exponent for the Wang-Tsiatis power spending function
rho results in more conservative
rho=3 is roughly equivalent to Obrien-Fleming
alpha linearly in the
An object of class
spending.function which is really a list
with the following components. The print method displays the original
Gives the spending function type, which is the character string "Pow"
the numeric value passed to the single argument,
returns the call
The print method returns the call by default
see references under
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## example 1: what is the result of calling a spending function ## A call to 'Pow' just returns the call Pow(rho=2) ## It does argument checking...the following results in an error: ## Not run: Pow() ## End(Not run) ## it doesn't matter whether the argument is named or not, ## either produces the same result Pow(2) ## but really its value is a list with a component named ## 'type' equal to "Pow", a component named 'rho' equal ## to the numeric value passed to the single argument 'rho' ## and a component named 'call' equal to the call. names(Pow(rho=2)) names(Pow(2)) Pow(rho=2)$type Pow(rho=2)$rho Pow(rho=2)$call ## example 2: ...But the intended purpose of the spending functions is ## in constructing calls to 'GrpSeqBnds' and to 'PwrGSD': frac <- c(0.07614902,0.1135391,0.168252,0.2336901,0.3186155, 0.4164776,0.5352199,0.670739,0.8246061,1) drift <- c(0.3836636,0.5117394,0.6918584,0.8657705,1.091984, 1.311094,1.538582,1.818346,2.081775,2.345386) test <- GrpSeqBnds(frac=frac, EfficacyBoundary=LanDemets(alpha=0.05, spending=Pow(2)), FutilityBoundary=LanDemets(alpha=0.10, spending=ObrienFleming), drift=drift)
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