请问大侠们，为什么我已经tsset id year 了 ，却还要求tsset?
. tsset id year
       panel variable:  id (strongly balanced)
        time variable:  year, 2000 to 2005
                delta:  1 unit
. levpet lv ,free(llab) proxy(lim) capital(lcap)
You must tsset your data or specify i() and t().
Mata run-time error
r(3499);