How to force R to use a specified factor level as reference in a regression?
问题 How can I tell R to use a certain level as reference if I use binary explanatory variables in a regression? It\'s just using some level by default. lm(x ~ y + as.factor(b)) with b {0, 1, 2, 3, 4} . Let\'s say I want to use 3 instead of the zero that is used by R. 回答1: See the relevel() function. Here is an example: set.seed(123) x <- rnorm(100) DF <- data.frame(x = x, y = 4 + (1.5*x) + rnorm(100, sd = 2), b = gl(5, 20)) head(DF) str(DF) m1 <- lm(y ~ x + b, data = DF) summary(m1) Now alter the