Suest after xtivreg2

Dear All,

I need to compare coefficients from 4 different regressions post xtivreg2. I am running:

quietly eststo: xtivreg2 cog x (vol=iv1) if (popfin==1), i(id) fe first
quietly eststo: xtivreg2 cog x (vol=iv2) if (popfin==1), i(id) fe first
quietly eststo: xtivreg2 cog x (vol=iv3) if (popfin==1), i(id) fe first
quietly eststo: xtivreg2 cog x (vol=iv4) if (popfin==1), i(id) fe first

I wish to compare the coefficients on vol from the four regressions above. I tried the following:

suest est1 est2 est3 est4, vce (cluster id)

but got the following error:
unable to generate scores for model est1
suest requires that predict allow the score option
r(322);


From researching further it seems (I am not 100% sure on this) suest requires predicted scores and xtivreg2 doesn't allow scores. So is there an alternative way to compare the coefficient on vol from the 4 estimates regressions above? Many thanks.

Sincerely,
Sumedha Gupta.