I am new to statistics and I understand that when a pattern can be found in the plots of the residuals and variables of a regression this is an indication that there is something which is missing from the regression.
I made a regression with two parameters, X1 and X2, for the regression I used: X1, X1^2, X2*X2, X2.
So far, I think there might be an error with X1^2, because there seems to be a slight curvature in the plot. All the others look fairly spread out around the horizontal axis.
What could I deduce from such plots ?
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