## Nonbinding futility rule [Two-Stage / GS Designs]

Dear Detlew,

The reference at page 19 actually refers to the CI futility criterion, but nevertheless the same argument should apply to the 'power of stage 1' criterion. Well, as I said: Formula (15), i.e. the formula for the estimated conditional target power is only defined if the power of stage 1, P(R

Best regards,

Ben.

PS: Please don't shoot the messenger

❝ If I see it correctly that's called in Maurer et al. *"futility rule can be applied in a nonbinding manner, ie, it can be used as guidance but must not necessarily be followed."* (page 19, bottom)

❝ How to obtain a sample size number for the second stage if we want to do so?

The reference at page 19 actually refers to the CI futility criterion, but nevertheless the same argument should apply to the 'power of stage 1' criterion. Well, as I said: Formula (15), i.e. the formula for the estimated conditional target power is only defined if the power of stage 1, P(R

_{1}), is less than the overall power 1 - beta. That's a key feature of the equation. Therefore, in my opinion the only possibility is: if you want to be able to handle it in a nonbinding manner, then you have to go with conditional error rates only (i.e. you cannot use the estimated conditional target power as target power for calculation of n2). So, we would need to select`ssr.conditional = "error"`

.Best regards,

Ben.

PS: Please don't shoot the messenger

### Complete thread:

- Finally: Exact TSD methods for 2×2 crossover designs Helmut 2018-04-21 17:17 [Two-Stage / GS Designs]
- Exact TSD methods: Example Helmut 2018-04-21 20:33
- Finally: Exact TSD methods for 2×2 crossover designs ElMaestro 2018-04-21 20:49
- Flow chart (without details) Helmut 2018-04-21 21:41
- naive questions regarding new functions in Power2Stage mittyri 2018-04-28 15:54
- Some answers Helmut 2018-04-28 17:29
- Some more "answers" d_labes 2018-04-29 21:11
- clarification regarding user Power2Stage guides mittyri 2018-04-30 13:41

- naive questions regarding new functions in Power2Stage mittyri 2018-04-28 15:54

- Flow chart (without details) Helmut 2018-04-21 21:41
- Technicality: Weigths for the inverse normal approach d_labes 2018-04-25 14:19
- Selection of w and w* Helmut 2018-04-26 09:51
- Selection of w and w* d_labes 2018-04-26 20:02
- Now what? w & w* examples d_labes 2018-05-09 13:53
- Now what? w & w* examples Ben 2018-06-10 20:12
- Now what? w & w* examples Helmut 2018-06-11 13:57
- Now what? w & w* examples Ben 2018-06-12 19:14

- a bug in interim.tsd.in()? mittyri 2018-06-11 23:27
- a bug in interim.tsd.in()? Ben 2018-06-12 19:32
- Nonbinding futility rule d_labes 2018-06-13 16:59
- Bad weather? Helmut 2018-06-13 19:23
- NLYW? d_labes 2018-06-14 10:18

- Nonbinding futility ruleBen 2018-06-13 20:26
- Nonbinding futility rule d_labes 2018-06-14 10:47
- Nonbinding futility rule Ben 2018-06-15 17:58
- Binding / Nonbinding futility rule - alpha control d_labes 2018-06-16 19:42
- Binding / Nonbinding futility rule - alpha control Ben 2019-03-30 09:52

- Binding / Nonbinding futility rule - alpha control d_labes 2018-06-16 19:42

- Nonbinding futility rule Ben 2018-06-15 17:58

- Nonbinding futility rule d_labes 2018-06-14 10:47

- Bad weather? Helmut 2018-06-13 19:23

- Nonbinding futility rule d_labes 2018-06-13 16:59

- a bug in interim.tsd.in()? Ben 2018-06-12 19:32

- Now what? w & w* examples Helmut 2018-06-11 13:57

- Now what? w & w* examples Ben 2018-06-10 20:12

- Selection of w and w* Helmut 2018-04-26 09:51