你的数据虽然是算不平衡面板数据,但是有些id对应的年份只有1年,而且还很多
还有你的T太小了,没有必要做单位根检验,你的数据是属于大N小T型的,可以直接用xtreg估计
For the asymptotic normal distribution of Z_t-tilde-bar to hold, T must be at least 5 if the dataset is strongly balanced and the deterministic part of the model includes only panel-specific means, or at least 6 if time trends are also included. If the data are not strongly balanced,then T must be at least 9 for the asymptotic distribution to hold. If these limits on T are not met, the p-value for Z_t-tilde-bar is not
reported.