title: backward elimination in R
body: <p>I am trying to get the final model using backward elimination with R but I got the following error message when I ran the code. Could anyone please help me this?</p>
  
  <pre><code>base&lt;-lm(Eeff~NDF,data=phuong)
  fullmodel&lt;-lm(Eeff~NDF+ADF+CP+NEL+DMI+FCM,data=phuong)
   step(full, direction = "backward", trace=FALSE )
  
  &gt; Error in step(full, direction = "backward", trace = FALSE) : 
  number of rows in use has changed: remove missing values?
  </code></pre>