Description Usage Arguments Details Value Note Author(s) References See Also Examples

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 `GrpSeqBnds`

and
`PwrGSD`

.

1 | ```
Pow(rho)
``` |

`rho` |
The exponent for the Wang-Tsiatis power spending function |

Larger `rho`

results in more conservative
boundaries. `rho`

=3 is roughly equivalent to Obrien-Fleming
spending. `rho`

=1 spends `alpha`

linearly in the
information fraction

An object of class `spending.function`

which is really a list
with the following components. The print method displays the original
call.

`type` |
Gives the spending function type, which is the character string "Pow" |

`rho` |
the numeric value passed to the single argument, |

`call` |
returns the call |

The print method returns the call by default

Grant Izmirlian

see references under `PwrGSD`

`LanDemets`

, `ObrienFleming`

, `Pocock`

,
`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 27 28 29 30 31 32 33 34 35 36 37 38 | ```
## 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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