Post3_A.r

library(car) 

#B2-B3=0
cVec<-c(0,0,1,-1) #this is L
car::linearHypothesis(mod_glm,cVec, verbose=TRUE, test = "Chisq")  #Estimated linear function (hypothesis.matrix %*% coef - rhs)
#Hypothesis matrix:
#     [,1] [,2] [,3] [,4]
#[1,]    0    0    1   -1

#Right-hand-side vector:
#[1] 0

#Estimated linear function (hypothesis.matrix %*% coef - rhs)
#[1] -0.07059217

#Linear hypothesis test

#Hypothesis:
#Gifts2 - Gifts3 = 0

#Model 1: restricted model
#Model 2: Respond ~ Gifts1 + Gifts2 + Gifts3

#  Res.Df Df  Chisq Pr(>Chisq)
#1  95409                     
#2  95408  1 0.6703      0.413



#Manually
(t(t(cVec)%*%mod_glm$coefficients)) %*%   solve((t(cVec)%*%vcov(mod_glm)%*%cVec))   %*%  (t(cVec)%*%mod_glm$coefficients)
#[1,] 0.6702656

#p-value
1-pchisq(0.6702656, 1)
#[1] 0.412959