Lag length Selection and Including Trend or not

[abdullah_alam]

Hi,

I just wanted some clarification on two issues.

(1) When we are running unit root tests on panel data (suppose IPS or LLC unit root test), we need to enter the lag length; in case we decide not to go by the automatic lag selection by AIC or SIC. How should we select the user-defined lag length for panel series?

(2) There is an option to include 'individual intercept', 'intercept and trend' and 'no trend'. How is that judged for the panel data as to which option we should include?

Just some basic help would do it.

Regards.