Tweeted By @yudapearl
1/ Great paper. First time I understand what "fixed effect" is. I used to confuse it with homogeneity, but Fig. 1 tells us it is an assumption of equality of two structural parameters which, in certain DAGs, lead to identification that otherwise will not be achieved. So simple, https://t.co/kvEHBPlWNg
— Judea Pearl (@yudapearl) July 29, 2019