I am using glmulti
to run hierarchical linear models and select the best model. I have 4 predictors (A
, B
, C
, D
) to the DV, and my goal is to run all main effect models plus all combination of interaction effects (i.e., A:B
, A:C
, A:D
). How do the following two models differ from each other?
library(glmulti)
# wrapper
glmer.glmulti <- function(formula, data, random = ""){
glmer(paste(deparse(formula), random), data = data, family = binomial)}
# model 1
glmulti(DV ~ A+B+C+D, level = 2, fitfunction = glmer.glmulti, random = "+ (1|ID)",
method = "g", data = df)
# model 2
glmulti(DV ~ A*B*C*D, level = 2, fitfunction = glmer.glmulti, random = "+ (1|ID)",
method = "g", data = df)
I know that "when an interaction between two factors is included in a model, then adding or not these factors as main effects does not change the model" (Calcagno, 2010). Seem that model 1 and model 2 should produce the same results because A*B*C*D
essentially includes the main effect of each predictor. But the two codes select a different best model.
Thanks!