Plans a group sequential trial (`GST`

)

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`K` |
number of stages |

`t` |
vector with the cumulative information fraction (default: (1:K)/K) |

`Imax` |
maximum information number (default: NULL) |

`SF` |
spending function (for details see below) |

`phi` |
parameter of spending function when SF=3 or 4 (See below) |

`alpha` |
alpha (type I error rate) |

`delta` |
effect size (alternative)(default: NULL) |

`pow` |
power (default: NULL) |

`compute.alab` |
specify if alpha-absorbing parameter values should be calculated (default: TRUE) |

`compute.als` |
specify if alpha-values ”spent” at every stage should be calculated (default: TRUE) |

The user has to specify either `Imax`

or `delta`

and `pow`

.
If all three items are specified, the pre-defined maximum information number is newly calculated from the information for `delta`

and `power`

, and `Imax`

is overwritten.

`SF`

defines the spending function.

`SF` = | 1 O'Brien and Fleming type spending function of Lan and DeMets (1983) |

`SF` = | 2 Pocock type spending function of Lan and DeMets (1983) |

`SF` = | 3 Power family (c_α* t^φ); `phi` must be greater than 0 |

`SF` = | 4 Hwang-Shih-DeCani family; (1-e^{-φ t})/(1-e^{-φ}), where `phi` cannot be 0 |

`plan.GST`

returns an object of the `class`

`GSTobj`

.
An object of class `GSTobj`

is a list containing the following
components:

`K` |
number of stages |

`a` |
lower critical bounds of group sequential design (are currently always set to -8) |

`b` |
upper critical bounds of group sequential design |

`t` |
vector with cumulative information fraction |

`al` |
alpha (type I error) |

`SF` |
spending function |

`phi` |
parameter of spending function when SF=3 or 4 (See below) |

`Imax` |
maximum information number |

`delta` |
effect size used for planning the primary trial |

Niklas Hack niklas.hack@meduniwien.ac.at and Werner Brannath werner.brannath@meduniwien.ac.at

Brannath, W, Mehta, CR, Posch, M (2008) ”Exact confidence bounds following
adaptive group sequential tests”, *Biometrics* accepted.

`GSTobj`

, `print.GSTobj`

, `plot.GSTobj`

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