title: Force inclusion of observations with missing data in lmer
body: <p>I want to fit a linear mixed-effects model using <code>lme4::lmer</code> without discarding observations with missing data. That is, I want <code>lmer</code> to go ahead and maximize the likelihood using all the data. </p>
  
  <p>Am I correct in thinking that using <code>na.pass</code> produces this behavior? <a href="http://grokbase.com/t/r/r-help/10afwwt9ja/r-using-na-action-na-pass-with-lmer-function" rel="nofollow">This unanswered question</a> is making me wonder if this might be wrong. </p>