Hello everyone，

There was a birth policy implemented only in urban area in 2015,and I’m trying to test the parallel trend of birth rate between hukou==1(urban area) and hukou==0(rural area) in 2013/2014/2016 so as to do difference in difference.

Here is my statistic and code:
Array
Array


I tried DID first and the result was fine,but when it comes to test the parallel trend(xtreg), it shows a lot of blanks:
Array

What might be the problem? If there is anything I don't make clear,please ask me.
Thank you so much.