Mistake Master
Actual Minus Predicted, in That Order
You'll learnthe residual as actual minus predicted and what its sign means, how to read one in context, what a residual plot is for, why random scatter is the good case, and how a curve in the residuals overrules any correlation.
A residual is what the model missed for one student, and it is computed in one order: actual minus predicted. Reverse the subtraction and every sign flips, so over-prediction and under-prediction trade places — this page draws both plots side by side and checks that each pair is an exact negation. Collected against the hours, the residuals answer a question the scatterplot answers less sharply and the correlation cannot answer at all: is a straight line the right shape. A cloud built from a curve still earns r = 0.925 here, and its residuals arch 8.9 points from ends to middle. The residual plot wins that argument every time. Twelve short steps; press Next for each one.