<p>我在做面板数据时，检验了存在异方差和自相关，之后我用了xtgls y x1 x2 ,panels(he) corr(psar1)去做回归，结果出现了<font color="#f70909">“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”。<font color="#000000">我不知这是什么意思？还请高手指点<br/></font><br/></font></p>