Bioequivalence and Bioavailability Forum • “Interim power”

“Interim power” [Two-Stage / GS Designs]

posted by Helmut – Vienna, Austria, 2013-10-08 16:58 (4210 d 09:48 ago) – Posting: # 11627
Views: 19,217

Hi Karthik,

❝ After completion of stage 1 we want to evaluate the power. If power is >= 80 evaluate BE at stage 1 (alpha=0.05) and if power < 80% evaluate BE at stage 1 (alpha=0.0294)

Yes, that’s “Method C”.

❝ After evaluation of power only we can plan further step.

Correct.

❝ In most of your lecture and discussion you mentioned No a posteriori Power.

That’s not a posteriori power, but part of the decision tree of the interim analysis. A posteriori would be after the study is completed (passing in stage 1 or in the combined analysis). See also what Potvin et al. state concerning their Example 2:

Using the data from both stages, we ﬁnd that the two-sided CI for the ratio (T/R) of geometric means at an α level of 0.0294 and DF = 17 is 88.45–116.38%, which meets the 80–125% acceptance criterion. We stop here and conclude BE, irrespective of the fact that we have not yet achieved the desired power of 80% (power = 66.3%).

(my emphasis)

❝ So In two stage study design how to evaluate the Power for our data.

After stage 1

Method C
fixed T/R 0.95, observed CV, n₁, α 0.05
Method B
fixed T/R 0.95, observed CV, n₁, α 0.0294

❝ Any validated method is there to evaluate the power for two stage study design or can I use PowerTOST or Winnonlin to evaluate the power.

PowerTOST is fine (see this example for Method B). Power in Phoenix/WinNonlin is wrong – don’t use it!

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Helmut Schütz

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Complete thread:

Potvin’s 2-stage adaptive design GSD 2012-08-17 20:56
- Potvin’s 2-stage adaptive design + RSABE/ABEL Helmut 2012-08-18 00:39
  - Potvin’s 2-stage adaptive design + RSABE/ABEL GSD 2012-08-31 16:30
    - Tough job Helmut 2012-08-31 18:37
      - Tough job GSD 2012-08-31 19:23
        
        C/D for EMA? Good luck! Helmut 2012-09-01 15:09
      - Surprise? d_labes 2012-09-05 12:57
        
        Got it. Ages for sims to complete Helmut 2012-09-05 13:35
        
        Life belt d_labes 2012-09-05 14:51
        
        Life belt Helmut 2012-09-05 15:20
  - Power for Two stage Design K2K 2013-10-07 14:43
    - Power for Two stage Design Helmut 2013-10-07 14:59
      - Power for Two stage Design K2K 2013-10-08 14:35
        
        “Interim power”Helmut 2013-10-08 14:58
        
        “Interim power” K2K 2013-10-09 12:39
        
        Validation of PowerTOST Helmut 2013-10-09 14:10
        Phoenix/WinNonlin - power d_labes 2013-10-09 16:11
        
        Phoenix/WinNonlin - power Helmut 2013-10-09 18:19
        
        power K2K 2013-10-10 08:36