I have ever read which mentioned that serial-correlation (or autocorrelation) in panel data, especially when the number of N is large and T is small, may ignore.
there are some reasons:
1. in panel data, ordering the data may affect the autocorrelation value. Panel data open the possibility of reordering in many ways, which affected the value of autocorrelation. But in time series data, the value of serial correlation is unique since we can't reorder data in many ways.
2. when the N is large and T is small, this data strongly faces heteroscedasticity than serial correlation. So the serial correlation is a minor problem.
Perhaps anybody can give me insight more into this issue? On how actually to deal with autocorrelation issue in panel data.