qFor a 2-predictor case: r1y = r2y = r12 = 0.50
q If only include one predictor (x1) (r2y = r12 =0) è R2=0.25
q By adding x2 in the regression (r2y = r12 =0.50) è R2=0.33
q In this case, the 2nd predictor improve the regression.
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qFor a 2-predictor case: r1y = r12 = 0.50 but r2y = 0.25
q If with only x1 è R2=025
q Adding x2 è R2=025 (still the same!!)
q In this case, the 2nd predictor is not useful.
It is because
q r2y £ r1y * r12 = 0.50*0.50 = 0.25
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