title: essentially perfect fit: summary may be unreliable in r
body: <p>I used the data for random effect model with panel data
  manager then I wrote this code with <code>plm</code> from package <code>plm</code>:</p>
  <pre><code>reffects &lt;- plm(efs~sps+fe+st+maj+exp+hw,data = data.p , model = &quot;random&quot;, 
    index = c(&quot;manager&quot;,&quot;time&quot;))
  </code></pre>
  <p>and this warning:</p>
  <pre><code> Warning messages:
  1: In summary.lm(object, ...) :
    essentially perfect fit: summary may be unreliable
  2: In summary.lm(object, ...) :
    essentially perfect fit: summary may be unreliable
  </code></pre>
  <p>I dont know how can I fix it? Is it related to the data?</p>