Confidence level and alpha with two one-sided t-tests (TOST) I'm making a non-inferiority study: two groups complete a test (where it is possible to score 0-30 points). I already have the test results for groupB. I want to investigate if groupA performs non-inferior to groupB, using two one-sided t-tests (TOST).
I chose an alpha=5%, and 95% CI. To get this, using TOST, I would have to specify a 90% CI / alpha=10%. Assessing non-inferiority I would only look at the lower CI, thus, my two-sided 90% CI would correspond to a one-sided 95% (and alpha=5%).
My question is: 1) is this correctly understood? And if so: 2) how would I formulate this correctly? My initial though is something like: "A two-sided 90% CI, alpha=0.10, corresponding to a one-sided 95%CI, alpha=0.05).
Thanks for your time.

you should set your confidence interval to 97.5% that way you get a one-sided 95% confidence interval and one-sided 5% alpha.
formulate it like this: a confidence interval of 97.5% was chosen and an alpha of 2.5% was set, resulting in the one-sided 95% confidence interval and one-sided 5% alpha.
