IE:DPC, Ch02: "Before" and "After" Perspectives of Data
Channel: David Kaplan
Date: 07/07/2020

Two perspectives: "before" = random variable, "after" = realized value.
Textbook (IE:DPC) "Introductory Econometrics: Description, Prediction, and Causality"
https://kaplandm.github.io/teach.html#IEDPC