title: Plot multiple ROC curves using ROCit
body: <p>I wanted to use ROCit for creating ROC curves. But I can not figure out, how to plot two ROC curves in the same plot.</p>
  
  <p>For example:</p>
  
  <pre><code>data("Diabetes")
  library(ROCit)
  plot(rocit(score = Diabetes$chol, class = Diabetes$dtest, negref = "-"))
  par(new=TRUE)
  plot(rocit(score = Diabetes$bmi, class = Diabetes$dtest, negref = "-"))
  </code></pre>
  
  <p>Using the <code>par</code> command in between, I can get it to work, but I would had to set the colors all manually and also the legend does not correctly reflect the data.</p>
  
  <p>Is it somehow possible to use ROCit to compare different models in the same plot?</p>