各位大牛，我用的xtabond2命令分别出现了一下两个warning，我看了一下论坛里好多帖子贴出的结果都有，是不是不影响结果呢？Warning: Number of instruments may be large relative to number of observations.Warning: Two-step estimated covariance matrix of moments is singular.
  Using a generalized inverse to calculate robust weighting matrix for Hansen test.
  Difference-in-Sargan/Hansen statistics may be negative.