source("http://www.uvm.edu/~rsingle/stat221/data/scripts-221.R")

 dat <- bookdata("ch05q02.txt")
 head(dat)
 
 y.x1x2 <- lm(SBP~QUET+AGE, data=dat)
 anova(y.x1x2) 
 
 y.x1 <- lm(SBP~QUET, data=dat)
 anova(y.x1)   
 
 
#Variable Added Last (VAL) tests vs. Variable In Order (VIO) tests
 summary(y.x1) #VAL test for Beta_1 matches anova(y.x1) for SLR
 anova(y.x1)   

 anova(y.x1x2)   #VIO tests for Beta_i
                 #VIO test  for Beta_2 (only) matches VAL test
 summary(y.x1x2) #VAL tests for Beta_i 

 y.x2x1 <- lm(SBP~AGE+QUET, data=dat)
 summary(y.x2x1) #VAL tests are     the same as y.x2x1 (order does NOT matter)
 anova(y.x2x1)   #VIO tests are NOT the same as y.x2x1 (order DOES     matter)
 anova(y.x1x2)   
 
 anova(y.x1)   



 y.x2 <- lm(SBP~AGE, data=dat)
 summary(y.x2)
 anova(y.x2) 
 
 y.x2x1 <- lm(SBP~AGE+QUET, data=dat)
 summary(y.x2x1)
 anova(y.x2x1)