在做聚类稳健标准差时,stata出现了这个提示:
Warning: estimated covariance matrix of moment conditions not of full rank.
model tests should be interpreted with caution.
Possible causes:
number of clusters insufficient to calculate robust covariance matrix
singleton dummy variable (dummy with one 1 and N-1 0s or vice versa)
partial option may address problem.
求助大神。