An investigator fits a regression model Y = X + $ to the data, and draws causal

An investigator fits a regression model Y = Xβ + $ to the data, and draws causal inferences from βˆ. A critic suggests that β may vary from one data point to another. According to a third party, the critique—even if correct—only means there is “unmodeled heterogeneity.”

(a) Why would variation in β matter?

(b) Is the third-party response part of the solution, or part of the problem?

Discuss briefly.