I want to test the difference between the coeffiecients on " huaf "and " lauf " which are ratios of high uncertainty avoiding individuals in a group and low uncertainty avoiding individuals in the group, respectively.

xtreg risk huaf i.year ,re vce (cluster msacode)

xtreg risk lauf i.year ,re vce (cluster msacode)

How can this be done after xtreg and also if I want to use xtivreg when I will need to include instrumental variables?

Thank you,