# lmer model simplification

I am trying to do model simplification looking at how different factors may affect distance. So I have snails kept in several habitats and I wanted to see if that affects how closely another snail may follow that snail. So I start off with this model:

  model1 <- lmer(sqrt(dist+6)~  (1|snail)+food+stress+food:stress+
weight+OriginalL+FollowedL)
summary(model1)


and the summary is this:

  Linear mixed model fit by REML ['lmerMod']
Formula: sqrt(dist + 6) ~ (1 | snail) + food + stress + food:stress +
weight + OriginalL + FollowedL

REML criterion at convergence: 561.1

Scaled residuals:
Min      1Q  Median      3Q     Max
-2.2941 -0.7698 -0.3347  0.7515  1.9564

Random effects:
Groups   Name        Variance Std.Dev.
snail    (Intercept) 0.000    0.000
Residual             2.334    1.528
Number of obs: 148, groups:  snail, 37

Fixed effects:
Estimate Std. Error t value
(Intercept)                    4.960927   0.662947   7.483
foodSweetPotato               -0.219039   0.357768  -0.612
stressshelter                 -0.246649   0.355999  -0.693
weight                         0.002520   0.063259   0.040
OriginalL                      0.015549   0.013072   1.189
FollowedL                     -0.008044   0.005972  -1.347
foodSweetPotato:stressshelter -0.300143   0.503215  -0.596

Correlation of Fixed Effects:
(Intr) fdSwtP strsss weight OrgnlL FllwdL
foodSwetPtt -0.309
stressshltr -0.315  0.502
weight      -0.615  0.008  0.009
OriginalL   -0.617 -0.021  0.032  0.123
FollowedL   -0.470  0.118  0.059  0.087 -0.004
fdSwtPtt:st  0.230 -0.707 -0.708 -0.008 -0.024 -0.055


Should I remove the least significant factor or remove the interactions first?

And after this is it a simple anova between my first model and most simplified model?

• Note, none of these issues are specific to lmer -- they are generic statistical modeling/inference questions – Ben Bolker Mar 25 '16 at 17:45

I'm not sure what you mean by "is it a simple anova between my first model and most simplified model"? If you want to do inference on the terms in the model, you can use a likelihood ratio test (implemented via anova() in R), or an F test, or ...