Linear Regression Feature Representations and High-Dimensional Modelling
Context
You are evaluating two linear regression specifications that use different feature representations derived from the same two original predictors x1 and x2.
Questions
-
Equivalence of feature representations
-
Model A: linear in the original features x1 and x2.
-
Model B: linear in the transformed features z1 = x1 + x2 and z2 = x1 − x2.
Are Model A and Model B equivalent in terms of the functions they can represent and the fitted predictions under ordinary least squares (OLS)? Provide a mathematical explanation.
-
High-dimensional linear modeling
-
If you have more than 1,000 predictors and want to fit a linear model, what problems might occur, and how would you mitigate them?