I recently played a ranked game, looked at the end game statistics, and noticed something odd with the enemy botlaner's vision scores:
http://i.imgur.com/Kzt1r20.png
Why is Morgana's vision score higher than Caitlyn's vision score, when Caitlyn placed more wards, destroyed more wards, and purchased more vision wards?
(Same with Vayne and Jarvan's vision scores)
Like this.
Having wards that last longer, and see enemies more often, will increase vision score more often.
If you place 20 wards, but they never see anyone before they expire, they aren't really worth much on vision score. Same with wards that are removed quickly (like can often happen with 
wards.
Also, vision granting abilities count, so if Morgana ulted a Vayne who was in her ult invisibility, it might count that since it grants true vision of enemies who get tethered.
