Code:
. xtmixed metabolism group##time || id:, var Performing EM optimization: Performing gradient-based optimization: Iteration 0: log likelihood = 121.88734 Iteration 1: log likelihood = 122.32628 Iteration 2: log likelihood = 122.32652 Iteration 3: log likelihood = 122.32652 Computing standard errors: Mixed-effects ML regression Number of obs = 67 Group variable: id Number of groups = 36 Obs per group: min = 1 avg = 1.9 max = 2 Wald chi2(5) = 15.46 Log likelihood = 122.32652 Prob > chi2 = 0.0086 ------------------------------------------------------------------------------ metabolism | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- group | 2 | -.0126059 .0162712 -0.77 0.438 -.0444968 .0192849 3 | .0139877 .0177918 0.79 0.432 -.0208836 .0488591 | 2.time | .0323302 .0159135 2.03 0.042 .0011403 .0635201 | group#time | 2 2 | -.0126164 .0223585 -0.56 0.573 -.0564382 .0312054 3 2 | -.0028619 .0243949 -0.12 0.907 -.0506751 .0449513 | _cons | .1481151 .0112525 13.16 0.000 .1260605 .1701697 ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ Random-effects Parameters | Estimate Std. Err. [95% Conf. Interval] -----------------------------+------------------------------------------------ id: Identity | var(_cons) | 3.38e-22 2.59e-21 1.02e-28 1.12e-15 -----------------------------+------------------------------------------------ var(Residual) | .0015194 .0002625 .001083 .0021318 ------------------------------------------------------------------------------ LR test vs. linear model: chibar2(01) = 0.00 Prob >= chibar2 = 1.0000