Example of using an offset in a linear model

OffsetInLinearModel.R

#offsets
#Simulate some data for this example
set.seed(12)
sig <- matrix(c(1.1,1,1,1.1),2,2)
df1<-data.frame(MASS::mvrnorm(n = 100, c(30,30), Sigma = sig ))
names(df1) <- c("x","y")

#Plot the data, and a 1:1 line
plot(df1$x,df1$y)
abline(0,1)

#Ordinary model with no offset.
#Slope summary gives statistics for difference from 0.
mod1 <- lm(y~x,data=df1)
summary(mod1)

#Ordinary model with no offset.
#Slope summary gives statistics for difference from 1.
mod2 <- lm(y~x+offset(x),data=df1)
summary(mod2)