如题,求:PPML估计的方法简介,使用情况及stata操作。1、在什么情况下用这种估计方法
2、stata 操作中
ppml estimation (the dummy z is correctly dropped, the observations with
z=1 are also dropped)
. ppml y x w z
ppml estimation with the keep option (the dummy z is correctly dropped but
no observations are dropped; this is equivalent to not conditioning on z)
. ppml y x w z, k
ppml estimation (v is correctly dropped, no observations are dropped
because v is not a dummy)
. ppml y x w v
都是在什么情况下用。