verstc Junior China, 20180226 10:15 Posting: # 18462 Views: 1,145 

Dear All, From the forum, I found the way to calculate intrasubject variability from confidence interval. I am wondering how I cite this calculation or anyone can tell me where this calculation originate from? Thanks, Shawn 
d_labes Hero Berlin, Germany, 20180226 12:26 @ verstc Posting: # 18464 Views: 1,007 

Dear shawn, » From the forum, I found the way to calculate intrasubject variability from confidence interval. Fine for you. If you are interested in a software for doing this, habe a look into R package PowerTOST / function CI2CV() .» I am wondering how I cite this calculation or anyone can tell me where this calculation originate from? This is a little bit algebra based on the formula of the CI. I don't think that there is a paper dealing with this algebra. I further think there is no need to have a citation for that. IIRC the little algebra was first mentioned in Helmut's lecture for the conference on "Bioequivalence and Bioavailability" Budapest 2009. — Regards, Detlew 
verstc Junior China, 20180226 13:41 @ d_labes Posting: # 18465 Views: 973 

Dear Detlew Thanks for your detailed response. best regards, Shawn Edit: Full quote removed. Please delete everything from the text of the original poster which is not necessary in understanding your answer; see also this post #5! [Helmut] 
Helmut Hero Vienna, Austria, 20180226 13:51 @ verstc Posting: # 18466 Views: 976 

Hi Shawn, no rocket science but basic algebra an 8^{th}grade pupil should be able to handle. I derived the formula about thirty years ago. _{} Hence, no reference… For background see this post and followings. If you want a reference for such a trivial calculation see this post. — Cheers, Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. ☼ Science Quotes 
Louis52 Junior 20180309 14:27 @ Helmut Posting: # 18510 Views: 544 

On this subject of finding the CV intra based on info from a previous study/paper, is there a function in Power.TOST or other package that would be something like CVfromCI but based on a DDI rather than BE? Let's say a DDI with one sequence for which we know the PE and CLs for the GMR (test vs. reference). 
Helmut Hero Vienna, Austria, 20180309 14:39 @ Louis52 Posting: # 18511 Views: 538 

Hi Louis, » […] something like CVfromCI but based on a DDI rather than BE? Let's say a DDI with one sequence for which we know the PE and CLs for the GMR (test vs. reference). One sequence? Are you thinking about a paired design? IMHO, DDI studies should be performed as crossovers. In paired designs you have to assume (!) that there are no period effects. However, if you have data of such a study, use e.g.,
BTW, the function CVfromCI() (alias CI2CV() ) supports all designs listed in known.designs() .— Cheers, Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. ☼ Science Quotes 
Louis52 Junior 20180309 15:13 @ Helmut Posting: # 18512 Views: 528 

Hi Helmut, I thought about the 'paired' design as I looked into known designs(), but I was not sure. Indeed the DDIs are COs but in several instances it happens that in period 1 a subject receives what is called the 'probe' while in period 2 it receives the "probe+investigational drug". I'm trying to find the CV intra associated with a particular "probe" based on DDI study in a published paper (no CV intra, just PE, CI, and N), as I need to use it in the sample size determination (precision only, no power) for a new DDI. Would 'paired' cover this situation? Of course, I can try to do it manually, but if it is already out there,...then why not use it. 
Helmut Hero Vienna, Austria, 20180309 15:42 @ Louis52 Posting: # 18513 Views: 543 

Hi Louis, » I thought about the 'paired' design as I looked into known designs(), but I was not sure. You were guessing right. » […] in several instances it happens that in period 1 a subject receives what is called the 'probe' while in period 2 it receives the "probe+investigational drug". Designed without consulting a statistician? Lacking period effects is a strong assumption. The only designs where a paired design is common is assessing linear PK of a new drug. Such a study starts with a single dose followed by saturation and another profile in (pseudo) steady state. Then we compare AUC_{0–τ} (MD) with AUC_{0–∞} (SD). Performing such a study as a crossover would be a logistic nightmare. Never ever have seen one. » I'm trying to find the CV intra associated with a particular "probe" based on DDI study in a published paper (no CV intra, just PE, CI, and N), as I need to use it in the sample size determination (precision only, no power) for a new DDI. Would 'paired' cover this situation? Yes. — Cheers, Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. ☼ Science Quotes 