Hi,
I try to model panel data with N=28 and T=15 (tsset number year). I have one binary variable in my explanatory variables. More, I want to add time dependency.
1) What is better- using time dummies (i.year) or time trend? If time trend, is it enough to add only variable year which can be treated as trend variable?
2) I try: a) pooled regression b)xtreg, fe c)xtreg, re d)xtgls. Is it good to add time dummies or trend in xtgls?
3) My data has heteroskedasticity, serial correlation and cross-correlation. Which method is better- xtreg, vce(robust) or xtgls? In xtgls how can I know which options choose corr(ar1) or corr(psar1)?

Thanks!