通过检验发现面板数据存在组内自相关和组间异方差，用指令<br>
preserve<br>
xtdata y x1 x2 x3 year ,fe clear<br>
xtgls y x1 x2 x3 x4 x5 x6 , p（h）corr（ar1)<br>
显示：year is not regularly spaced or does not have intervals of delta -- use the force option to treat the intervals as though they were regular<br>
请问该怎么做？