[R] (lme4) p-values for single terms in mixed models involved in sig interactions

sarah hoffmann s.hoffmann85 at outlook.com
Sat Jul 6 19:21:22 CEST 2013

I am using lme4 to fit a mixed effects model to my data. I have a significant interaction between two variables. My question is what is the correct way to get p-values for single terms involved in that interaction. 
I have been using stepwise backwards deletion and model comparisons to get p-values,and refitting the model using a REML approach to get estimates.However, presumably to get the p values for single terms, I also have to remove the interaction as well, and therefore inaccurate. 
I have confused myself with this now, as to whether in this case you should compare a model with the interaction and the single term of interest removed to the minimum adequate model (in which case the p values are over inflated for the single terms), or whether to remove the interaction from the minimum adequate model, and then compare this to an updated model, with the single term removed.
This is an example of what the model would look like:

##to get p values for e.g. temp

###but what's the correct way to get p value for brood_size or weight?

Your help would be greatly appreciated...thanks! 		 	   		  

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