I have a register with 500 patients treated according to the old guideline and 300 patients treated according to the new guideline. The success of treatment is measured by a continuous variable Y. Under the new guideline Y after treatment should be generally lower compared to the old guideline.
Which group of patients did achieve lower Y values and which did not?
I started with a quantile regression Y_aftertreatement ~ (Y_beforetreatement+age+gender+conf2+conf3+…+confn)*guidline
Where guidline=1 if new guideline and guidline=0 old guideline.
I thought the significant interaction terms conf2*guideline (etc.) would tell me which patient characteristics profit from the new guideline and which do not.
Is there a better approach? How do I include medication? Medication (dose) also changed with the guidelines.
I am grateful for any tip.