42. Regression Score: Training Data

Question:

Imagine you were a less savvy machine learner, and didn’t know to test on a holdout test set. Instead, you tested on the same data that you used to train, by comparing the regression predictions to the target values (i.e. bonuses) in the training data. What score do you find? You may not have an intuition yet for what a “good” score is; this score isn’t very good (but it could be a lot worse).