Yes but no but yes but no but… [RSABE / ABEL]

posted by Helmut Homepage – Vienna, Austria, 2013-03-29 16:10 (2967 d 03:23 ago) – Posting: # 10312
Views: 18,112

Hi Martin!

» what about defining the extent of scaling after interim analysis of the first stage data (CV estimated in 1st stage) within a group-sequential adaptive design?

Theoretically OK. ;-)

» Drawback: BUT what if the CV at interim is smaller than 0.3 ... :confused:

or it is larger than 0.3 in stage 1 and in the pooled data set (n↑ = more precise estimate) you find one which is ≤0.3? If the inflation is real (still not sure) we have a problem – only with EMA’s method – in the CV-range 0.3–0.5. IMHO there are two options:
  1. Iteratively adjust α. :-D
  2. Use a fixed α of ~0.030 for partial replicates and ~0.025 for full replicates if CVWR ≤0.5 (see plots above). This should cover the entire range of designs and sample sizes of up to 96. The maximum ad­just­ment (at 0.3) is almost in­de­pendent from sample size (see plot below). Conservative for any CV >0.3…


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