Bioequivalence and Bioavailability Forum • Sandwich

Sandwich - Simsalabim [🇷 for BE/BA]

posted by d_labes – Berlin, Germany, 2010-04-28 12:58 (5111 d 02:42 ago) – Posting: # 5253
Views: 56,124

Dear Helmut,

----- Sandwich -----

❝ you have already outed yourself as a passionate wheel-reinventer, but why don't you simply go with the Welch-test (orwhatsover for unequal variances)?

To cite myself near the beginning of this thread: "I would go for a parallel groups study with exactly 2 groups with the 'simple' t-test (Welch variant ...)". Simple was here meant with respect to the lme() model used in bear.

But I'm seeking for something that can be generalized easily to more then 2 groups. Pairwise tests I'm not so happy with.

Eventually this (recently discovered) could be a way:
Herberich E, Sikorski J, Hothorn T (2010)
"A Robust Procedure for Comparing Multiple Means under Heteroscedasticity in Unbalanced Designs"
PLoS ONE 5(3): e9788. doi:10.1371/journal.pone.0009788
online resource

Easy to implement in R, only a couple of code lines.
But I was not a sandwich gourmet up to now :-D

.

----- Simsalabim -----
<nitpicking>

❝ ...

❝ lnPKT <- rnorm(n=nT,mean=MeanT,sd=CVT*MeanT)

❝ lnPKR <- rnorm(n=nR,mean=MeanR,sd=CVR*MeanR)

❝ ...

If you are really interested in dealing with log-transformed metrics as lnPK suggests :-D

I would suggest you the following modification:

# short hand function

   CV2sd <- function(CV) return(sqrt(log(1.0 + CV^2)))

...

     lnPKT  <- rlnorm(n=nT, mean=log(MeanT), sd=CV2sd(CVT)) 

     lnPKR  <- rlnorm(n=nR, mean=log(MeanR), sd=CV2sd(CVR))

Of course this will not affect the comparison between t-test with equal variances and Welch t-test I think.
</nitpicking>

—
Regards,

Detlew

Complete thread:

Parallel bears meeting at random in infinity d_labes 2010-04-22 11:43 [🇷 for BE/BA]
- Parallel bears meeting at random in infinity ElMaestro 2010-04-22 12:53
  - Parallel groups in bear - CIs d_labes 2010-04-22 14:00
    - Parallel groups in bear - CIs ElMaestro 2010-04-22 21:47
      - Parallel groups in bear - CIs d_labes 2010-04-23 09:09
    - Parallel groups in bear - CIs yjlee168 2010-04-25 23:29
- Parallel bears meeting at random in infinity yjlee168 2010-04-22 23:09
  - Modelling Parallel bears d_labes 2010-04-23 09:12
    - Modelling Parallel bears yjlee168 2010-04-23 21:14
      - Validating vs. WinNonlin... Helmut 2010-04-24 00:28
        
        Validating vs. WinNonlin... yjlee168 2010-04-24 19:36
        Validating vs. WinNonlin... yjlee168 2010-04-26 00:09
        
        Validating vs. WinNonlin... Helmut 2010-04-26 01:29
        
        WNL in replicate BE yjlee168 2010-04-26 08:59
        
        WNL in replicate BE Helmut 2010-04-26 16:15
      - Modelling Parallel bears yjlee168 2010-04-25 19:34
        
        Modelling Parallel bears ElMaestro 2010-04-25 20:40
        Dataset Helmut 2010-04-25 22:38
        
        Dataset yjlee168 2010-04-25 22:44
        
        Dataset Helmut 2010-04-26 01:13
        
        Dataset yjlee168 2010-04-26 08:16
        
        NCA → Statistical analysis for parallel study Helmut 2010-04-26 13:12
        
        NCA → Statistical analysis for parallel study yjlee168 2010-04-26 18:43
        
        dilemma yjlee168 2010-04-26 08:41
        Equal variances d_labes 2010-04-26 09:04
        
        Equal variances yjlee168 2010-04-26 09:22
        
        GLM = Equal variances d_labes 2010-04-26 13:29
        
        GLM = Equal variances Helmut 2010-04-26 14:45
        
        I'm a believer d_labes 2010-04-26 15:58
        
        I'm a believer Helmut 2010-04-26 16:31
        
        Equal variances Helmut 2010-04-26 12:55
        
        gls() for unequal variances? d_labes 2010-04-26 16:36
        
        gls() for unequal variances? Helmut 2010-04-26 17:00
        Sims Helmut 2010-04-27 01:36
        
        Sandwich - Simsalabimd_labes 2010-04-28 10:58
        
        Sandwich - Simsalabim Helmut 2010-04-28 14:19
        parametrization of R function rlnorm martin 2010-05-02 18:22
        
        Mean of log-normal d_labes 2010-05-03 16:22
        parametrization of R function rlnorm ElMaestro 2013-07-26 21:42
        
        Martin‽ Helmut 2013-07-28 02:01