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RegisterPooling: example [Power / Sample Size]
posted by Helmut 
– Vienna, Austria, 2010-12-23 17:11 (5294 d 16:39 ago) – Posting: # 6338
Views: 13,186
Dear Kim!
OK.
See the examples (slides 18–20).
In a 2×2 cross-over study you have 2 sequences (TR|RT). Therefore, with a sample size of \(\small{n}\) we have \(\small{df=n-2}\).
In my first example (slide 18), first study: \(\small{n=12}\), \(\small{df=12-2=10}\), \(\small{CV=0.2\;(20\%)}\), \(\small{\sigma^2=\log_{e}(CV^2+1)=\log_{e}(0.04+1)\approx0.0392}\), weighted variance \(\small{\sigma_\textrm{w}^2=\sigma^2\times df\approx 0.3922}\).
Repeat these steps for all studies and calculate the “total variance weighted by df” \(\small{\sigma_\textrm{tot}^2}\). In the example that’s \(\small{(0.3922+0.8618)/(10+10)=0.0627}\). Then \(\small{CV_\textrm{pooled}=\sqrt{\exp(\sigma_\textrm{tot}^2)-1}\approx0.2544}\). No need for M$-Excel.
❝ I know "Calculate the variance from CV"
OK.
❝ I don't know "Calculate the total variance weighted by df"
❝ Naturally I don't know "Calculation the pooled CV from total variance"
❝ How is the calculate the total variance?
❝ I want explain this by Excel or Electronic File 
See the examples (slides 18–20).
In a 2×2 cross-over study you have 2 sequences (TR|RT). Therefore, with a sample size of \(\small{n}\) we have \(\small{df=n-2}\).
In my first example (slide 18), first study: \(\small{n=12}\), \(\small{df=12-2=10}\), \(\small{CV=0.2\;(20\%)}\), \(\small{\sigma^2=\log_{e}(CV^2+1)=\log_{e}(0.04+1)\approx0.0392}\), weighted variance \(\small{\sigma_\textrm{w}^2=\sigma^2\times df\approx 0.3922}\).
Repeat these steps for all studies and calculate the “total variance weighted by df” \(\small{\sigma_\textrm{tot}^2}\). In the example that’s \(\small{(0.3922+0.8618)/(10+10)=0.0627}\). Then \(\small{CV_\textrm{pooled}=\sqrt{\exp(\sigma_\textrm{tot}^2)-1}\approx0.2544}\). No need for M$-Excel.
—
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Helmut Schütz
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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:
- How is the calculated Sample Size? bjkim97 2010-12-22 02:42 [Power / Sample Size]
![[Mix]](https://static.bebac.at/img/mix.png "open in Mix view")
- How is the calculated Sample Size? boonchai_l 2010-12-22 05:55
- How is the calculated Sample Size? VRP 2010-12-22 06:54
- How is the calculated Sample Size? bjkim97 2010-12-22 07:40
- How is the calculated Sample Size? boonchai_l 2010-12-22 09:06
- How is the calculated Sample Size? Dr_Dan 2010-12-22 11:06
- HVDs/HVDPs: global harmonization?! Helmut 2010-12-22 16:59
- How is the calculated Sample Size? boonchai_l 2010-12-22 09:06
- Pantoprazole CVs d_labes 2010-12-22 12:05
- Pantoprazole CVs boonchai_l 2010-12-22 21:26
- Expectation ElMaestro 2010-12-22 22:22
- Opinions Ohlbe 2010-12-23 01:23
- Pooling... Helmut 2010-12-23 15:29
- Choosing CVs d_labes 2011-01-03 08:43
- Pantoprazole CVs bjkim97 2010-12-23 14:43
- Pooling: exampleHelmut 2010-12-23 16:11
- Pantoprazole CVs boonchai_l 2010-12-22 21:26
- How is the calculated Sample Size? boonchai_l 2010-12-22 05:55
Ing. Helmut Schütz