# Ch5-Pocock: The Pocock Alpha Spending Function In PwrGSD: Power in a Group Sequential Design

## Description

Stipulates alpha spending according to the Pocock spending function in the Lan-Demets boundary construction method. Its intended purpose is in constructing calls to `GrpSeqBnds` and `PwrGSD`.

## Usage

 `1` ```Pocock() ```

## Value

An object of class `spending.function`

 `type` Gives the spending function type, which is the character string "Pocock" `call` returns the call

## Note

The print method returns the call by default

Grant Izmirlian

## References

see references under `PwrGSD`

`LanDemets`, `ObrienFleming`, `Pow`, `GrpSeqBnds`, `PwrGSD`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26``` ```## example 1: what is the result of calling a spending function ## A call to 'Pocock' just returns the call Pocock() ## but really its value is a list with a component named ## 'type' equal to "Pocock" and a component named ## 'call' equal to the call. names(Pocock) Pocock()\$type Pocock()\$call ## example 2: ...But the intended purpose of the spending functions its ## intended purpose 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=Pocock), FutilityBoundary=LanDemets(alpha=0.10, spending=ObrienFleming), drift=drift) ```