Solved – calculating regression sum of square in R

multiple regressionrregression

Here is sample data:

        brainIQ <- 
      read.table (file= "https://onlinecourses.science.psu.edu/stat501/sites/
  onlinecourses.science.psu.edu.stat501/files/data/iqsize.txt",
     head = TRUE)

I am trying to fit multiple linear regression.

mylm <- lm(PIQ ~  Brain + Height + Weight, data = brainIQ)
anova(mylm)

Default function anova in R provides sequential sum of squares (type I) sum of square. 

Analysis of Variance Table

Response: PIQ
          Df  Sum Sq Mean Sq F value  Pr(>F)  
Brain      1  2697.1 2697.09  6.8835 0.01293 *
Height     1  2875.6 2875.65  7.3392 0.01049 *
Weight     1     0.0    0.00  0.0000 0.99775  
Residuals 34 13321.8  391.82                  
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

I belief, thus the SS are Brain, Height | Brain, Weight | (Brain, Weight) and residuals respectively.

Using package car we can also get type II sum of square. 

library(car)
Anova(mylm, type="II")
Anova Table (Type II tests)

Response: PIQ
           Sum Sq Df F value    Pr(>F)    
Brain      5239.2  1 13.3716 0.0008556 ***
Height     1934.7  1  4.9378 0.0330338 *  
Weight        0.0  1  0.0000 0.9977495    
Residuals 13321.8 34                      
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Here sum of squares are like: Brian | (Height, Weight), Height | (Brain, Weight), Weight | (Brain, Height).

Which look pretty like Mintab output:

enter image description here

My question is how can I calculate the regression row in the above table in R ?

Best Answer

SS(Regression) = SS(Total) - S(Residual)

You can get SS(Total) by:

SSTotal <- var( brainIQ$PIQ ) * (nrow(brainIQ)-1)
    SSE     <- sum( mylm$resid^2 )
SSreg   <- SSTotal - SSE

The degrees of freedom for the "Regression" row are the sum of the degrees of freedom for the corresponding components of the Regression (in this case: Brain, Height, and Weight).

Then to get the rest:

dfE   <- mylm$df.residual
dfReg <- nrow(brainIQ) - 1 - dfE
MSreg <- SSreg / dfReg
MSE   <- SSE / dfE
Fstat <- MSreg / MSE
pval  <- pf( Fstat , dfReg, dfE , lower.tail=FALSE )
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