title: What is "NA * variable" in lavaan package in R? (factor analysis)
body: <pre><code>library(lavaan)
  
  #model
  
  fig2.5.data &lt;- '
  1
  .5 1
  .1 .1 1
  .2 .3 .2 1
  '
  
  fig2.5.cor &lt;- getCov(fig2.5.data, names=c(c(&quot;X1&quot;, &quot;X2&quot;, &quot;X3&quot;, &quot;X4&quot;)))
  
  fig2.5.model &lt;- '
  # latent variables
  F1 =~ NA*X1 + a*X1 + b*X2
  F2 =~ NA*X3 + c*X3 + d*X4
  
  # variances/covariances
  
  # fix variance to 1
  F1 ~~ 1*F1
  
  # fix variance to 1
  F2 ~~ 1*F2
  F1 ~~ e*F2
  
  # label residual variances
  X1 ~~ w*X1
  X2 ~~ x*X2
  X3 ~~ y*X3
  X4 ~~ z*X4
  </code></pre>
  <p>It's an extract from the textbook I'm reading at the moment.</p>
  <p>I understand everything else but &quot;NA*&quot; parts.</p>
  <p>What are they?</p>
  <p>I've encountered many NAs when using R, such as when there are missing data, but this one seems to be totally incomprehensible to me.</p>
  <p>Any help would be much appreciated!</p>