title: lmer Error: number of observations < number of random effects
body: <p>I am trying to run an <code>LMM</code> allowing time to be a random effect:</p>
  
  <pre><code>lmer(efficacy ~ time + (1+time|id), data=long, REML=TRUE)
  </code></pre>
  
  <p>However, I get the error messageas below:</p>
  
  <blockquote>
    <p>Error: number of observations (=3948) &lt;= number of random effects (=4496) for term (1 + time | id); the random-effects parameters and the residual variance (or scale parameter) are probably unidentifiable</p>
  </blockquote>
  
  <p>I have three time points but not all subjects have data for all 3 time points (attrition) but my missing count on my outcome variable (efficacy) only had 13 missing values and I have a total number of <code>3961 participants</code> in my entire data set. If anyone can shed some light on this or point me in the right direction I'd much appreciate it. </p>
  
  <p>Thanks.</p>