title: Plotting partial effects with confidence intervals for lmer models
body: <p>I would like to plot the partial effects of the terms in my model. </p>
  
  <p>I used the <code>effects</code> package which is supposed to work on <code>lmer</code> models, however I get an error related to the class of the model object.</p>
  
  <p>The following is a reproducible example:</p>
  
  <pre><code>library(lme4)
  library(effects)
  
  fm1 &lt;- lmer(Reaction ~ Days + (Days|Subject), sleepstudy) #sleepstudy is an example dataset in lme4   
  
  plot(effect("Days", fm1))
  # Error in plot(effect("Days", fm1)) : 
  #   error in evaluating the argument 'x' in selecting a method for function 'plot': Error in # UseMethod("effect", mod) : 
  #  no applicable method for 'effect' applied to an object of class "c('lmerMod', 'merMod')"
  </code></pre>
  
  <p>What am I doing wrong?</p>