Reducing scatter plots to a coherent function via MSE.
Multiple regression testing is a method to derived which weights for a weighted average produces the minimum Mean Squared Error. How to perform MRT wasn’t covered in the text. Guess and check seems like a fine enough approach to begin with. Calculus if you want, sure.
Regression testing is a technique in which a scatter plot of data can be reduced to a single function approximating the scatter. This is done using the Mean Squared Error (Mean Squared Error) technique. Whatever function produces the minimal MSE is the best function… and the size of the minimum MSE is an indicator of system variability (aka Noise).
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Mean squared error - Wikipedia