gets a profile of a GLM using offset

glm_profile.R

library(dplyr)

adf <- data.frame(x=1:100) %>%
  mutate(y=rnorm(100, 5*x, 90))

#What do we have
plot(adf)

#examine the output
summary(glm(y ~ x, data=adf))

#try out two different fixed slope coefficients
glm(y ~ 1, offset=2*x, data=adf)
glm(y ~ 1, offset=1*x, data=adf)


### Fit a bunch of slope coefficients to make a profile
### for the intercept
coefFrame <- data.frame(b1 = seq(-30,30,length.out=500)) %>%
  rowwise() %>%
  mutate(int = coef(glm(y ~ 1, offset=b1*x, data=adf)),
         LL = logLik(glm(y ~ 1, offset=b1*x, data=adf))[1])

plot(LL ~ b1, data=coefFrame)

critVal <- logLik(glm(y ~ x, data=adf))[1]-qchisq(.95,1)/2

coefFrame %>%
  filter(LL>critVal) %>%
  slice(c(1,n()))