Calculate Cutoff value

Hello,

I think what you're after is foremost z scores and then looking at drawing inference. I suggest having a look here: https://www.statology.org/z-score-r/ (for basic z scores) and then a bit more involved article here on that with significant testing here: https://replicationindex.com/2019/03/31/one-tail-or-two-tails-that-is-the-question/