Monday, October 17 Linear Regression
When X and Y are perfectly correlated zy = zx When X and Y are perfectly correlated
We can say that zx perfectly predicts zy zy’ = zx Or zy = zx ^
When they are imperfectly correlated, i.e., rxy ≠ 1 or -1 zy’ = rxyzx
Example from hands…
When we want to express the prediction in terms of raw units: zy’ = rxyzx Y’ = bYXX + aYX bYX = rYX (σy / σx) aYX = Y - bYXX _ _
Explained and unexplained variance SStotal = SSexplained + SSunexplained SStotal = SSexplained + SSunexplained N
Explained and unexplained variance r2XY = 1 - σ2Y’ [ =unexplained] σ2Y [ =total] σ2Y - σ2Y’ = σ2Y r2 is the proportion explained variance to the total variance.