clear
set obs 50
generate z = rnormal() // this is the random effect
generate id = _n
expand 2
generate x = runiform(-5,5)
generate y = 3 + 2*x + z + rnormal()

mixed y x || id:
estimates store orig

summarize x
display _b[x]*r(sd)
display _b[_cons]+_b[x]*r(mean)
generate xcntr = x - r(mean)
egen xstd = std(x)

mixed y xcntr || id:
estimates store centered
mixed y xstd || id:

estimates table orig centered .