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RegisterInter and Total Variability [Power / Sample Size]
posted by Helmut 
– Vienna, Austria, 2011-09-11 13:55 (4990 d 00:45 ago) – Posting: # 7346
Views: 13,333
Dear Benjamin,
answering only your first question (now) …
Not always (see below).
What it your drug/formulation is ‘unusual’? If you have only a parallel study you simply don’t know.
OK, here are the complete data of the previous post (only the two extremes):*
If you base the sample size estimation in a X-over on \(\sigma_{intra}^2\approx\sigma_{total}^2/2\) you would end up with CVintra of
answering only your first question (now) …
❝ […] But what about just taking intra variance to be half of the total variance (when only total variance is given)? This approach seems to be a conservative estimate.
Not always (see below).
❝ Usually intra variance is less than or equal to inter variance.
What it your drug/formulation is ‘unusual’? If you have only a parallel study you simply don’t know.
❝ It also makes sense coming from the correlation between two responses on the same subject, which is equal to 1/2 if and only if the within variance equals the between variance. Based on this one can calculate CVs. Or not? (the Lansoprazole example should also fulfill this)
OK, here are the complete data of the previous post (only the two extremes):*
Study CVintra CVinter CVtotal intra/total MSEw MSEB MSEt
Methylphenidate 7.00% 19.13% 20.41% 34.27% 0.004882 0.076746 0.039225
Lansoprazole 47.01% 25.14% 54.60% 86.09% 0.199667 0.322229 0.262708If you base the sample size estimation in a X-over on \(\sigma_{intra}^2\approx\sigma_{total}^2/2\) you would end up with CVintra of
14.07% (↑) for methyphenidate and 37.47% (↓) for lansoprazole. In the former case you waste money – in the latter you blew the study.- See this post for corrections.
—
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Helmut Schütz
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The quality of responses received is directly proportional to the quality of the question asked. 🚮
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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:
- Inter and Total Variability Ben 2011-09-02 13:43 [Power / Sample Size]
![[Mix]](https://static.bebac.at/img/mix.png "open in Mix view")
- Inter and Total Variability Helmut 2011-09-02 14:21
- Inter and Total Variability Ben 2011-09-03 11:28
- Inter and Total Variability Ben 2011-09-08 19:22
- Inter and Total VariabilityHelmut 2011-09-11 11:55
- Inter and Total Variability Ben 2011-09-13 22:03
- Inter and Total Variability Helmut 2011-09-14 00:43
- Inter and Total Variability Ben 2011-09-18 12:36
- Inter and Total Variability Ben 2011-10-06 18:51
- Inter-subject variance sasophylistic (GLM vs. MIXED) d_labes 2011-10-07 13:33
- Inter and Total Variability Helmut 2011-09-14 00:43
- Inter and Total Variability Ben 2011-09-13 22:03
- Inter and Total Variability ElMaestro 2011-09-18 14:14
- Inter and Total Variability Ben 2011-09-19 19:43
- Inter and Total VariabilityHelmut 2011-09-11 11:55
- Inter and Total Variability Ben 2011-09-08 19:22
- Inter and Total Variability Ben 2011-09-03 11:28
- Inter and Total Variability Helmut 2011-09-02 14:21
Ing. Helmut Schütz