Bioequivalence and Bioavailability Forum • Variance=0

Variance=0 [RSABE / ABEL]

posted by Helmut – Vienna, Austria, 2013-05-03 18:07 (4008 d 06:45 ago) – Posting: # 10535
Views: 21,837

Dear Detlew!

❝ Please note the 'Variance' parameter in case of AUCinf.

… and the negative one obtained in PHX. Seems that SAS’ RLME-engine forces negative values to zero.

❝ See this post to notice that we really need 'Variance'=0 in our model (Type CS is only an approximation to that end, hoping the 'Variance' parameter is fitted with a value near zero).

Ooh – that one. :-D

❝ So we eventually have the optimizer to tell that for AUCt.

I’m not very optimistic whether this is possible in PHX at all; I will ask Pharsight. In PHX for linear mixed effects models the initial estimates are derived by the method of moments:
log AUCt

Starting estimates of variance parameters: csDiag_11 0.00881650 csBlock_11 0.188267 Var(Period*Formulation*Subject)_21 0.0519883 Var(Period*Formulation*Subject)_22 0.0703479

log AUCi

Starting estimates of variance parameters: csDiag_11 -0.00961080 csBlock_11 0.148549 Var(Period*Formulation*Subject)_21 0.0620715 Var(Period*Formulation*Subject)_22 0.0894799

Alternatively one can state initial variances. If I set csDiag_11 (PHX’ terminology) to zero (whilst keeping the others), the optimizer iterates happily around (four iterations instead of two) – only to end up with the same final estimates…

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
Helmut Schütz

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Complete thread:

FDA's HVD SAS Code from Progesterone Guidance jag009 2013-04-22 16:39 [RSABE / ABEL]
- Proc MIXED vs. Proc GLM Helmut 2013-04-22 17:47
  - Proc MIXED vs. Proc GLM jag009 2013-04-22 20:33
    - SAS vs. PHX Helmut 2013-04-22 22:10
      - SAS vs. PHX Shuanghe 2013-04-23 11:45
        
        SAS vs. SAS d_labes 2013-04-23 16:50
        
        SAS vs. SAS vs. Phoenix Helmut 2019-11-12 13:01
      - SAS vs. PHX jag009 2013-04-23 15:56
        
        SAS Warning (Note) on Proc Mixed jag009 2013-04-23 17:07
        
        Nut Job.. jag009 2013-04-30 21:09
        
        Second opinion (PHX 6.3) Helmut 2013-05-01 16:21
        
        Second opinion (PHX 6.3) jag009 2013-05-01 17:16
        
        Second opinion (PHX 6.3) ElMaestro 2013-05-01 18:48
        In praise of a full replicate Helmut 2013-05-01 19:16
        Third opinion d_labes 2013-05-02 12:00
        
        Compound Symmetry Helmut 2013-05-02 14:41
        
        Compound Symmetry - SASian (1) d_labes 2013-05-02 16:26
        
        Variance=0Helmut 2013-05-03 16:07