Multirating free version sort posts

Hi,
I have question how can I sort posts by multirating score?
The idea is to use HTML filter form in order to let user sort posts by multiple parameters, like date, title and rating:

<form class='post-filters'>
	<select name="orderby">
		<?php
			$orderby_options = array(
				'post_date' => 'Order By Date',
				'post_title' => 'Order By Title',
				'mr_rating_result_star_rating' => 'Order By Rating',
			);
			foreach( $orderby_options as $value => $label ) {
				echo "<option ".selected( $_GET['orderby'], $value )." value='$value'>$label</option>";
			}
		?>
	</select>
	<input type='submit' value='Filter!'>
</form>

But I have no idea how to sort by Multirating plugin rating results and how data is stored in plugin.