I'm revising a paper for a peer-reviewed medical journal. Part of our analysis included creating "quartiles" out of two continuous variable (distance and volume). We used the function "xtile" and allowed it to create these automatically

The reviewer is requesting clarification on how these cut points were chosen, and if they are the ideal outpoints for the data.

I have not been able to find the exact method by which xtile selects the cut points. My understanding is it chooses the optimal cut points automatically, based on the distribution of the data - I may be completely wrong.

Is there a way in which I can convey this to the reviewer. And/or is there a more robust methods to determine these cut points?

Thanks!