Imph ☆ Algeria, 20211020 11:03 (48 d 09:47 ago) Posting: # 22643 Views: 708 

Hi, I would like to know please which formula to choose to calculate the number of subjects among all the formulas published: Dilleti, Chow, Julious,... For now I am using chow's formula, I would like to know if there is a plausible reference that supports its use. Thank you. 
Helmut ★★★ Vienna, Austria, 20211020 11:36 (48 d 09:14 ago) @ Imph Posting: # 22644 Views: 629 

Hi Imph, » […] which formula to choose to calculate the number of subjects among all the formulas published: Dilleti, Chow, Julious,... Diletti (1981), which is exact based on Owen’s Q function. Julious is based on an approximation by the noncentral tdistribution and fine as well. » For now I am using chow's formula, I would like to know if there is a plausible reference that supports its use. Don’t. Chow’s is based on the shifted central tdistribution and the paper contains typos. See also this post. I suggest to estimate sample sizes with functions of the package PowerTOST . All three methods are implemented, where the exact one is the default.Whilst in many cases sample sizes based on the shifted central tdistribution will be equal to the others, sometimes estimated sample sizes are larger than necessary. The background is shown in an article. — Diftor heh smusma 🖖 Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes 
Imph ☆ Algeria, 20211020 12:53 (48 d 07:58 ago) @ Helmut Posting: # 22647 Views: 593 

Thank you very much for your answer. From where I am, I was unable to access dileti's publications. Can you please help me get them. I thank you in advance 
Helmut ★★★ Vienna, Austria, 20211020 13:26 (48 d 07:24 ago) @ Imph Posting: # 22648 Views: 594 

Hi Imph, » Thank you very much for your answer. Welcome. » From where I am, I was unable to access dileti's publications. Can you please help me get them. Check your inbox. Two points:
PowerTOST is Open Source (licensed under GPL3), comes at no cost, was used in numerous publications, textbooks, and even by the … — Diftor heh smusma 🖖 Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes 
Imph ☆ Algeria, 20211024 10:41 (44 d 10:10 ago) @ Helmut Posting: # 22654 Views: 487 

Thank you so much. Your response has been of great help. I have a few more questions if I may:
Thank you in advance. 
Helmut ★★★ Vienna, Austria, 20211024 10:54 (44 d 09:57 ago) @ Imph Posting: # 22655 Views: 515 

Hi Imph, » Thank you so much. Your response has been of great help. Welcome. » – By consulting Dileti's paper, I noticed that there is no formula for the calculation of the number of subjects. Is there a way or a reference to get the formula please. You can only calculate power for a given sample size, i.e., you start with an assumption and then increase (or decrease) n to obtain at least the target power. See there for the details. Step by step:
In PowerTOST ’s sample size functions you can show the iterations by setting the argument details to TRUE (by default only the final result is shown):
» – […] in the calculation of the degrees of freedom, for example (2n2), where "n" has to be estimated. I would like to know on what basis this "n" is estimated. See above. — Diftor heh smusma 🖖 Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes 
d_labes ★★★ Berlin, Germany, 20211024 19:26 (44 d 01:24 ago) @ Imph Posting: # 22656 Views: 484 

Dear Imph, beside to all what Helmut has told you you may find in the /doc directory of the package a PDF file "BE_power_sample_size_excerpt.pdf" which has some small further informations about the sample size estimation. You may obtain an approximation of n by using the large sample approximation. See P. Zhang “A simple formula for sample size calculation in equivalence studies.” J. Biopharm. Stat. 2003 Aug;13(3):52938 This approximate number is in many cases relatively close to the exact value, and is used in PowerTOST as starting value of the iterative search of the sample size. — Regards, Detlew 