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Lack-of-fit sum of squares and Pure-error sum of squaresStats/Inferential 2020. 2. 4. 12:17
1. Overview
In statistics, a sum of squares due to lack of fit, or more tersely a lack-of-fit sum of squares, is one of the components of a partition of the sum of squares of residuals in an analysis of variance, used in the numerator in an F-test of the null hypothesis that says that a proposed model fits well. The other component is the pure-error sum of squares.
2. Description
2.1 Intuition
SSE=SSPE+SSLF
∑(observedvalue−fittedvalue)2(error)=∑(observedvalue−localaverage)2(pureerror)+∑(weight×(localaverage−fittedvalue)2(lackoffit)
2.1.1 The sum of squares due to "pure" error (SSPE)
The sum of squares of the differences between each observed y-value and the average of all y-values corresponding to the same x-value.
2.1.2 The sum of squares due to lack of fit (SSLF)
The weighted sum of squares of differences between each average of y-values corresponding to the same x-value and the corresponding fitted y-value, the weight in each case being simply the number of observed y-values for that x-value.
2.2 Formular
n∑i=1ni∑j=1ˆε2ij=n∑i=1ni∑j=1(Yij−ˆYi)2=n∑i=1ni∑j=1(Yij−ˉYi)2⏟sumofsquaresduetopureerror+n∑i=1ni(ˉYi−ˆYi)2⏟sumofsquaresduetopureerror
3. Reference
https://en.wikipedia.org/wiki/Lack-of-fit_sum_of_squares
https://www.youtube.com/watch?v=6VhjGw90TB4
http://reliawiki.org/index.php/Simple_Linear_Regression_Analysis
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