title: R: Error in eval(predvars, data, env) : numeric 'envir' arg not of length one in intrinsic.pars() in multgee package
body: <p>I have a data frame <code>df</code>with the following data:</p>
  
  <pre><code>family_id_cass   twin_order  ls75cat
    10026          1           2
    10026          2           2
    10071          1           3
    10071          2           3
    10132          1           1
    10132          2           2
  </code></pre>
  
  <p>I would like to run <code>intrinsic.pars()</code>, so what I am doing is the following:</p>
  
  <p><code>intrinsic.pars(df$ls75cat, df$family_id_cass, df$twin_order, rscale="ordinal")</code> but i get the following error:</p>
  
  <p><code>Error in eval(predvars, data, env) : 
    numeric 'envir' arg not of length one</code></p>
  
  <p>What am I doing wrong? </p>