Question Let user sort posts based on rating

Hello, I found this bit of code that makes a dropdown box, letting the users sort posts based on date or title. what I need is to let my users sort posts based on wpdiscuz ratings or date. what parameter should I add to the code instead of title? thanks!

<form action="" method="get">
<select name="sort" id="sorting">
  <option value="title" <?php if ($sort == "title"){ echo 'selected="selected"'; } ?> >Sort by title</option>
  <option value="date" <?php if ($sort == "date"){ echo 'selected="selected"'; }?> >Sort by publication date</option>
</select>
<input type="submit" value="Submit" /></form>