clear
set obs 50
generate zi = rnormal(0,2) // this is a random intercept
generate zs = rnormal() // this is a random slope
generate id = _n
expand 5
generate res = rnormal() // residual

generate x = runiform(-5,5)
generate y = 3 + 2*x + zi + zs*x + res
// Here, y=3+2*x is the fixed effect,
//   y = zi + zx*x are random effects,
//   and y = res is the residual/error term.
//   In total we have y = fixed + random + residual.

regress y x
estimates store under
mixed y x || id:
estimates store rint
mixed y x || id: x
estimates store rslope

estimates table under rint rslope, stats(ll)

lrtest rslope rint

mixed y x || id: x, cov(uns)
lrtest . rslope

summarize x
display _b[_cons] + _b[x]*r(mean)
display _b[x]*r(sd)
display (_se[x]*r(sd))

egen xstd = std(x)
mixed y xstd || id: xstd, cov(uns)