Hi Chris,

I had assumed it would be by membership number, but on the link I provide to my site, it doesn't seem to do that.

Actually, this "Sort by popularity" is sorted by how many "hit" the group have. As you can see on this table"*_social_cluster", where got i column named "hit". I have tested these in my local and checked on it codes.

For better view
codes:

		$sortItems->popular->url = ESR::groups(array_merge($sortUrls, array('ordering' => 'popular')));

on Database
http://screencast.com/t/3f3CN7ps
on "sort by popularity"/frontend
http://screencast.com/t/MzoNQx5J

Please advice.

OK that makes sense. Thank you!

You are most welcome