## Estimation of CVw and/or CVwR [Power / Sample Size]

Hi Alyssa,

» Usually ISCV result of the 3 way crossover or 4 way crossover, replicate study published in the PAR is CVwR or CVw?

There are no rules (it depends on what the assessor decides to include of the study report). However, since the study was a replicate design with reference-scaling,

We can estimate the CV

~~Since this does not match what is given in the PAR, it is a strong hint that the 42.6% is the CV~~.

[Nonsense, not a Williams’ design! See ElMaestro’s post and the correction.]

If the expanded limits are given in the PAR, you can estimate the CV

I agree with Dan but want to add one point. In my experience the variability

PS: Avoid sample size “calculation” if you don’t mind. Use “estimation” instead.

PPS: The partial replicate is a lousy design. If you want to have only three periods I suggest the 2×2×3 full replicate TRT|RTR instead. If you insist in the partial replicate (why?), use the function

» Usually ISCV result of the 3 way crossover or 4 way crossover, replicate study published in the PAR is CVwR or CVw?

There are no rules (it depends on what the assessor decides to include of the study report). However, since the study was a replicate design with reference-scaling,

*possibly*it is CV_{wR}(more important).We can estimate the CV

_{w}with the R-package`PowerTOST`

:`library(PowerTOST)`

~~round(100*CVfromCI(lower = 0.9625, upper = 1.2511,~~

~~n = 41, design = "3x6x3"), 1)~~

~~Unbalanced 3x6x3 design. n(i)= 7/7/7/7/7/6 assumed.~~

[1] 36.8

_{wR}

[Nonsense, not a Williams’ design! See ElMaestro’s post and the correction.]

If the expanded limits are given in the PAR, you can estimate the CV

_{wR}from the*upper*limit by the function`CVwRfromU()`

to check. Example for 136.4%:`round(100 * CVwRfromU(136.4 / 100), 1)`

[1] 42.6

_{wT}is not accessible in a partial replicate design, CV_{w}< CV_{wR}means that the test is less variable than the reference (since CV_{w}is pooled from CV_{wR}and CV_{wT}).I agree with Dan but want to add one point. In my experience the variability

*across*studies (with the same clinical setup, bioanalytical method,_{}) tends to be more “stable” than the T/R-ratio. Hence, don’t fall into the trap of believing the nice 98.7% you observed in the pilot study. It might well have been pure chance. For HVD(P)s assuming a T/R-ratio of better than 90–111% is not a good idea (recommended by the two Lászlos* and therefore, the default in functions`sampleN.scABEL()`

and `sampleN.RSABE()`

of `PowerTOST`

).PS: Avoid sample size “calculation” if you don’t mind. Use “estimation” instead.

PPS: The partial replicate is a lousy design. If you want to have only three periods I suggest the 2×2×3 full replicate TRT|RTR instead. If you insist in the partial replicate (why?), use the function

`sampleN.scABEL.sdsims()`

. Slower than `sampleN.scABEL()`

but more accurate. For a comparison see the vignette and scroll down to “Heterogenicity”.- Tóthfalusi L, Endrényi L.
*Sample Sizes for Designing Bioequivalence Studies for Highly Variable Drugs.*J Pharm Pharmaceut Sci. 2011;15(1):73–84. open access.

—

Helmut Schütz

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

Science Quotes

*Dif-tor heh smusma*🖖Helmut Schütz

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

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### Complete thread:

- Sample size calculation (Pilot study result vs literature) Alyssa 2020-05-04 04:35
- Sample size calculation (Pilot study result vs literature) Dr_Dan 2020-05-04 08:46
- Sample size calculation (Pilot study result vs literature) Alyssa 2020-05-04 09:26

- Estimation of CVw and/or CVwRHelmut 2020-05-04 12:07
- Estimation of CVw and/or CVwR ElMaestro 2020-05-04 12:14
- Mea culpa! Helmut 2020-05-04 12:40
- It must be Myco ElMaestro 2020-05-04 13:46
- It is, it is! Helmut 2020-05-04 14:07
- It is.... Alyssa 2020-05-05 05:00
- Tutorial Helmut 2020-05-05 12:45
- Tutorial Alyssa 2020-05-08 06:48
- library d_labes 2020-05-08 11:16
- Tutorial (from the start) Helmut 2020-05-08 13:08
- Tutorial (from the start) Alyssa 2020-05-12 04:05
- Tracking down error Helmut 2020-05-12 11:49
- Tracking down error: stringsAsFactors d_labes 2020-05-13 11:34
- R <4.0.0 Helmut 2020-05-13 12:07
- R <4.0.0 ElMaestro 2020-05-13 14:18
- R <4.0.0 🔚 Helmut 2020-05-13 14:21

- PowerTOST’s functions with as.character(design) d_labes 2020-05-13 18:50
- PowerTOST’s functions with as.character(design) Helmut 2020-05-13 18:55

- R <4.0.0 ElMaestro 2020-05-13 14:18

- R <4.0.0 Helmut 2020-05-13 12:07
- Tracking down error Alyssa 2020-05-15 05:08
- All’s well that ends well. Helmut 2020-05-15 10:52

- Tracking down error: stringsAsFactors d_labes 2020-05-13 11:34

- Tracking down error Helmut 2020-05-12 11:49

- Tutorial (from the start) Alyssa 2020-05-12 04:05

- Tutorial Alyssa 2020-05-08 06:48

- Tutorial Helmut 2020-05-05 12:45

- It is.... Alyssa 2020-05-05 05:00

- It is, it is! Helmut 2020-05-04 14:07

- It must be Myco ElMaestro 2020-05-04 13:46

- Mea culpa! Helmut 2020-05-04 12:40

- Estimation of CVw and/or CVwR ElMaestro 2020-05-04 12:14

- Sample size calculation (Pilot study result vs literature) Dr_Dan 2020-05-04 08:46