title: How to get a prediction interval for a lmer object?
body: <p>I've surfed the web and haven't found a satisfactory answer for this. </p>
  
  <p>How would I generate a prediction interval for from a lmer object for each observation in the test dataset?</p>
  
  <pre><code>train_ind &lt;- sample(seq(1:nrow(iris)), size = nrow(iris)/2, replace = F)
  TRAIN &lt;- iris[train_ind,]
  TEST &lt;- iris[-train_ind,]
  
  m1 &lt;- lmer(Sepal.Length ~ Sepal.Width + Petal.Length + (1|Species), data = TRAIN)
  </code></pre>
  
  <p><code>interval</code> has no argument with predict. <code>sim</code> apparently doesn't work so I need to use an mcmc function that comes with LMER and draw from quantiles? </p>