请问xtpmg的回归结果怎么看啊，是上面的_ec部分，还是下面的SR部分，分别是什么意思啊？请赐教~

pmg|mg|fe selects the desired estimation procedure. pmg estimates the
        pooled mean-group model where the long-run effects, beta, are
        constrained to be equal across all panels.  The short-run coefficients,
        including phi, are allowed to differ across panels. mg estimates the
        mean-group model where the coefficients of the model are calculated
        from the unweighted average of the unconstrained, fully heterogeneous
        model. fe estimates the dynamic fixed effects model where all
        parameters, except intercepts, are constrained to be equal across
        panels.  pmg is the default.

为什么我输入命令后，会出现 insufficient  obersavation?