# Stage 1-evaluation step of GSED

### Description

`stage_1_evaluation`

is used to evaluate the efficacy of the subgroup selected at the end of the first stage of GSED.

### Usage

1 | ```
stage_1_evaluation(keep, Z_1j, f, u)
``` |

### Arguments

`keep` |
Vector containing the indices of the subgroups selected at stage 1. |

`Z_1j` |
Vector containing the Z-statistics (standard normal under H0) for each subgroup. Must be of length |

`f` |
Vector containing the prevalence rates of each subgroup. |

`u` |
Vector containing the upper boundaries for stagewise decisions. |

### Value

A list is returned, consisting of:

`stage` |
Integer containing the current step. Value is 1 by default, or -1 if the trial stops earlier for efficacy after this evaluation step. |

`S` |
Vector containing the indices of the subgroups selected at stage 1 (= |

### Author(s)

Marie-Karelle Riviere-Jourdan eldamjh@gmail.com

### References

Baldur P. Magnusson and Bruce W. Turnbull. Group sequential enrichment design incorporating subgroup selection. Statistics in Medicine, 2013. <doi:10.1002/sim.5738>

### Examples

1 | ```
stage_1_evaluation(keep=c(2,3), Z_1j=c(-0.49,1.07,1.44), f=c(0.6,0.2,0.2), u=c(2.7625,2.5204))
``` |