inst/snippet/taste-anova06.R

In rpruim/fastR: Foundations and Applications of Statistics Using R (2nd Edition)

NTaste <- data.frame(score = TasteTest$score,
                     scr   = as.numeric(TasteTest$scr) - 1,
                     liq   = as.numeric(TasteTest$liq) - 1,
                     scrliq = ( as.numeric(TasteTest$scr) -1 ) * 
                              ( as.numeric(TasteTest$liq) -1 )
                     );  NTaste

Omega <- lm(score ~ scr * liq, data= TasteTest)
M <- model.matrix(Omega)
M2 <- cbind(M[, 3], M[, 2] - 2 * M[, 4])
M3 <- cbind(M[, 2], M[, 3] - 2 * M[, 4])

omega1  <- lm(score ~ scr + liq, data = TasteTest)
omega2  <- lm(score ~ M2, data = TasteTest)
omega2a <- lm(score ~ liq + I(scr - 2 * scrliq), data = NTaste)
omega3  <- lm(score ~ M3, data = TasteTest)
omega3a <- lm(score~ scr + I(liq - 2 * scrliq), data = NTaste)

anova(omega1, Omega)   # test for interaction
# test main effect for scr
# anova(omega2a, Omega)  # this gives the same result as line below
anova(omega2, Omega)   
# test main effect for liq
# anova(omega3a, Omega)  # this gives the same result as line below
anova(omega3, Omega)