Sample size calculation when comparing two coefficients of variation


I am a medical student, wanting to start a clinical study between two devices. Since I want to compare especially on precision and reproducibility, I am going to use the coefficient of variation. I already have the CV of one of the devices from another published article (14,6%) and have calculated the other device will give me a CV of 11%.
Which method do I use to calculate my sample size that is needed to power this study? At this moment I use G*Power for my calculations.

Thank you and have a great weekend.


Active Member
is the measurement continuous, count, normal, lognormal or what? Need to have some idea of that. I'd suggest that this will work out best under log-normal model.


Well-Known Member
Assuming you want to show that the second is more precise than the first, you can use a Monte Carlo approach. Choose a possible sample size n. Generate n normal(100, 11). Calculate CV for your sample. Record 1 if the sample CV is less than 14.6% else 0. Repeat many times. The average of the 0, 1s is the power. If it is too low, increase the sample size and try again. This is a one tailed test as it stands.