If you are having trouble connecting to the SSC servers, the Stata Journal server is an excellent backup.

xtset firm_id year

Run the following commands in your Stata command window to download and install the package:

Remember:

), you reject the null hypothesis. This indicates that your panel data suffers from serial correlation, which can bias your standard errors and lead to inefficient estimates. 5. Address Serial Correlation

Use the xtgls command, which can explicitly model the correlation structure.

xtserial sales investment capital