在 MuMIn::dedge 的结果中获取“+”号

Question

I am trying to MuMIn::dredge linear mixed-effect models lme4::lmer with categorical/continuous variables, the code is as follows:

# Selection of variables of interest
sig<-c("Age", "Sex", "BMI", "(1|HID)", "h_age", "h", "h_g", "smk_hs")
# Model formula
formula<-paste0("log10_PBA_N", "~", paste0(c(sig), collapse="+"))
# Global model
model<-lmer(formula, data=data)
# Dredging
DRG<-dredge(global.model=model)

The code runs fine (I guess), but in the results, I have this:

 Global model call: lmer(formula = formula, data = data)
---
Model selection table 
      (Int)      Age       BMI h h_age h_g Sex smk_hs df   logLik  AICc  delta weight
2   -0.2363 -0.01421                                   4 -332.476 673.0   0.00  0.847
66  -0.2461 -0.01420                                +  5 -333.689 677.5   4.47  0.090
34  -0.2406 -0.01417                         +         5 -334.508 679.2   6.11  0.040
4   -0.3348 -0.01598  0.007096                         5 -335.935 682.0   8.96  0.010
18  -0.1553 -0.01421                     +             7 -334.310 682.9   9.84  0.006
98  -0.2493 -0.01416                         +      +  6 -335.723 683.6  10.60  0.004
68  -0.3463 -0.01599  0.007206                      +  6 -337.140 686.5  13.43  0.001

Can someone please explain to me, what does the "+" sign mean in the results?

Answer 1

I recently had the exact same question and was struggling to find an answer. However, based on a response to a similar question asked on R Studio Community , I think the answer is simply that a '+' sign means that a given categorical variable term is included as significant in that particular model.

So, looking at your table, the first model only includes the intercept, the second includes the intercept and the smk_hs categorical variable, the third includes the intercept and the Sex variable, etc.