“classical” GSD alpha's [Two-Stage / GS Designs]

posted by d_labes  – Berlin, Germany, 2015-12-03 10:47 (3358 d 18:47 ago) – Posting: # 15692
Views: 13,373

(edited on 2015-12-03 16:19)

Dear Helmut, dear Ben!

Two-sided or not two-sided, that is the question!

library(ldbounds)
# two-sided, check via summary()
bds2.poc <- bounds(t=c(0.5,1), iuse=c(2,2), alpha=rep(0.025,2))
summary(bds2.poc)
2*(1-pnorm(bds2.poc$upper.bounds))

gives us:
[1] 0.03100573 0.02774015

# one-sided
bds1.poc <- bounds(t=c(0.5,1), iuse=2, alpha=0.05)
summary(bds1.poc)
1-pnorm(bds1.poc$upper.bounds)

gives us:
[1] 0.03100573 0.02972542
simsalabim Ben's preferred values.

I personally opt for two-sided :cool:.

BTW: Lan/deMets spending function is Pocock like.
Nearer to original Pocock are the mean of the critical values. Try
2*(1-pnorm(rep(mean(bds2.poc$upper.bounds),2)))
simsalabim, Pocock's natural constant! Nearly.
(1-pnorm(rep(mean(bds1.poc$upper.bounds),2)))
hokus pokus fidibus, Ben's magical number!

Regards,

Detlew

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