## CV-intra # 60% CV-inter [Power / Sample Size]

Dear Nav,

I’m not in my office, so be a little patient to get a thorough response – first I have to read your 66 pages of statistics.

Just for completeness (because you sent me the paper by private mail):

We’ll handle that…

Hey, that’s

Examples

again as

I’m not in my office, so be a little patient to get a thorough response – first I have to read your 66 pages of statistics.

Just for completeness (because you sent me the paper by private mail):

Julious SA. *TUTORIAL IN BIOSTATISTICS. Sample sizes for clinical trials with Normal data.*

Stat Med. 2004;23(12):1921–86. doi:10.1002/sim.1783.

❝ Well, I am not sure how to estimate the sample size for a parallel design?

We’ll handle that…

❝ Re: 60% of inter to estimate the intra: I am a statistician and I routinely see the PK individuals taking 60% of inter to be the intra for estimating sample size for a crossover design and always wondered about the validity of the approach.

Hey, that’s

**!***black magick*Examples

- Imagine two studies; one with very tight inclusion criteria with respect to anthrompometric covariates (sex, BMI, age, …), the other one very ‘liberal’. CV
_{inter}(but not CV_{intra}!) will be higher in the first one; just my 2*¢*.

- If I remember it correctly, diltiazem is a compound with low to moderate intra-subject CV (about 15%), but much higher CV
_{inter}.

- Extreme examples are all studies employing different phenotypes. Whereas the phenotype is time-invariant – we don’t change our genotype in the washout – the intra-subject variability may be horrible (20fold differences in C
_{max}are not uncommon).

- Although you may have established some kind of intra-/inter-CV ratio, this most likely is not –
*only*– a property of the compound / formulation(s), but also of the study’s design/performance.

- No, not 60%, rather 25%…

- Again from my aging memory: buspirone CV
_{intra}~15%, CV_{inter}>80%?

❝ 60% of inter to estimate the intra

again as

**.***black magick*—

Helmut Schütz

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

Science Quotes

*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:

- Sample size estimation for parallel design Nav Coelho 2007-07-20 16:14 [Power / Sample Size]
- Parallel designs (total variance) Helmut 2007-07-20 16:29
- Parallel designs (total variance) Nav Coelho 2007-07-20 18:38
- CV-intra # 60% CV-interHelmut 2007-07-22 01:17
- total (pooled) variance: examples Helmut 2007-07-23 17:44
- total (pooled) variance: examples Nav Coelho 2007-07-23 19:58
- total (pooled) variance: examples BEQool 2023-04-18 09:59
- Higher-Order Crossovers Helmut 2023-04-20 10:19
- Higher-Order Crossovers BEQool 2023-04-21 07:53

- total (pooled) variance: examples zizou 2023-04-21 21:23
- total (pooled) variance: examples BEQool 2023-04-22 18:20
- total (pooled) variance: examples zizou 2023-04-22 21:06
- total (pooled) variance: examples BEQool 2023-04-25 10:57
- total (pooled) variance: examples zizou 2023-04-25 22:43
- total (pooled) variance: examples BEQool 2023-05-04 08:17

- total (pooled) variance: examples zizou 2023-04-25 22:43

- total (pooled) variance: examples BEQool 2023-04-25 10:57

- total (pooled) variance: examples zizou 2023-04-22 21:06

- total (pooled) variance: examples BEQool 2023-04-22 18:20

- Higher-Order Crossovers Helmut 2023-04-20 10:19

- Parallel designs (total variance) Nav Coelho 2007-07-20 18:38
- Sample size estimation for parallel design Dipesh Jayswal 2007-07-24 08:52

- Parallel designs (total variance) Helmut 2007-07-20 16:29