CVtotal ≠ CVintra + CVinter [Power / Sample Size]
❝ In a bioavailability study with six healthy volunteers:
I would never plan a pivotal study based on results of such a small pilot – especially if the variability is high. Let’s assume a CV of 30%. From six subjects we can calculate a confidence interval of the CV with 18–102%. Not meaningful.
❝ ...(Cmax; range 135–422 ng ml-') and time to maximum (tmax; range 1.5–7.0 h) for the three tablet doses showed significant differences between subjects (P <0.009; between subject coefficients of variation (CVs) 34% and 27%, respectively). There were no within subject differences in C, (P = 0.32; mean within subject CV 11%
The quoted text leaves many questions open. I guess it was a crossover. Significant differences between subjects… Why report this at all? Since we know that results come from different subjects, this effect will
![[image]](img/uploaded/image485.png)
❝ To calculate the sample size for a parallel study I use the total CV= 45?
No way! CVs are not additive (CVpooled ≠ CVintra + CVinter). See the methylphenidate example from this post.
MSe MSs CVintra CVinter CVpooled
0.004882 0.07675 7.00% 19.1% 20.4%
❝ or do I need the pooled variability?
Yes.
❝ Which is?
Not the slightest idea. Not accessible from what you posted. You need either the complete ANOVA or the raw data.
Dif-tor heh smusma 🖖🏼 Довге життя Україна!
![[image]](https://static.bebac.at/pics/Blue_and_yellow_ribbon_UA.png)
Helmut Schütz
![[image]](https://static.bebac.at/img/CC by.png)
The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes
Complete thread:
- Extrapolation john john 2015-05-13 13:36 [Power / Sample Size]
- CVinter (or CVtotal) from CVintra Helmut 2015-05-13 14:33
- CVinter (or CVtotal) from CVintra nobody 2015-05-13 14:53
- OT: Drug Res Helmut 2015-05-13 15:11
- OT: Drug Res nobody 2015-05-13 15:18
- completely OT Helmut 2015-05-13 15:29
- completely OT nobody 2015-05-13 15:37
- completely OT Helmut 2015-05-13 15:29
- OT: Drug Res nobody 2015-05-13 15:18
- OT: Drug Res Helmut 2015-05-13 15:11
- CVinter (or CVtotal) from CVintra john john 2015-05-14 12:16
- CVtotal ≠ CVintra + CVinterHelmut 2015-05-15 13:05
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 13:13
- CVtotal ≠ CVintra + CVinter Helmut 2015-05-15 13:14
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 13:50
- CVtotal ≠ CVintra + CVinter Helmut 2015-05-15 14:07
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 15:07
- CVtotal ≠ CVintra + CVinter Helmut 2015-05-15 15:10
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 15:07
- CVtotal ≠ CVintra + CVinter Helmut 2015-05-15 14:07
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 13:50
- CVtotal ≠ CVintra + CVinter Helmut 2015-05-15 13:14
- CVtotal ≠ CVintra + CVinter john john 2015-05-15 13:13
- CVtotal ≠ CVintra + CVinterHelmut 2015-05-15 13:05
- CVinter (or CVtotal) from CVintra nobody 2015-05-13 14:53
- CVinter (or CVtotal) from CVintra Helmut 2015-05-13 14:33