Bioequivalence and Bioavailability Forum

Equal variances [🇷 for BE/BA]

posted by Helmut  – Vienna, Austria, 2010-04-26 14:55 (5891 d 18:37 ago) – Posting: # 5231
Views: 67,886

Dear D. Labes,

❝ ❝ boxplot(lnAUC0t ~ drug, col="lightgray", yl)

❝ Ooops: > Error in eval(expr, envir, enclos) : object 'yl' not found

Shit! Of course instead of
boxplot(lnAUC0t ~ drug, col="lightgray", yl)
use
boxplot(lnAUC0t ~ drug, col="lightgray")

❝ A very fine example of hetero-scedasticity and eventually of non-normality .

Maybe. But we are not allowed to test that anyhow.
For non-bears, here is the dataset (imbalanced, 27 subjects) for download.

❝ With t-test assuming equal variances one gets:

❝          Point Estimate   CL90 lower   CL90 upper


❝ Ratio           101.61        83.31       123.92

❝

❝ Homework: Compare this to the results of lm() or lme() in this thread

❝ .

Yes, sure. What else? That's why we should avoid it.

❝ To repeat my question above: Any hint for more then 2 groups?

❝ Very seldom for BE studies, I know. But according to Murphy's law I have to deal with a 3-parallel-group design already tomorrow.

I went through the literature last week and did not come to a conclusion yet. Essentially there are two approaches:

• one-way ANOVA with post-hoc tests
  
• between group t-tests

So if you want to get an opinion for tomorrow: I would go with Welch-tests, because ANOVA (or lm and lme) assume homoscedasticity. See also:

Moser BK, Stevens GR. Homogeneity of variance in the two-sample means test. Amer Statist. 1992;46:19-21.

Depending on the study’s target I would consider a Bonferroni-adjustment (that’s even the original application: independent tests).

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


The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

Complete thread:

• Parallel bears meeting at random in infinity d_labes 2010-04-22 11:43 
  • 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 variancesHelmut 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 - Simsalabim d_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