Function Package / Library Model Type Outcome Variable Multilevel Typical Use
lm() base R (stats) Linear model Metric / continuous No Standard regression with independent observations
glm() base R (stats) Generalized linear model Binary, count, proportions, etc. No Logistic regression, Poisson regression
lmer() lme4 Linear mixed-effects regression Metric / continuous Yes Multilevel regression with continuous outcome
glmer() lme4 Generalized linear mixed-effects regression Binary, count, proportions, etc. Yes Multilevel logistic or Poisson regression