User blog comment:Dj0z/AP on supports - quick analysis/@comment-72.224.16.55-20120510052849

This is really a poor use of math. Consider what you're really doing when you just add together ratios. You're saying "1 more point of AP on this champion will do _____ more damage/heal/shield." Even if we can assume that 1 point of damage, 1 point of healing, and 1 point of shielding are equally valuable, your formula doesn't work.

When Sona uses Hymn of Valor, 1 more AP doesn't make her deal 0.7 extra damage, it makes her deal 1.4 extra damage because 2 targets take damage. When Janna uses Howling Gale, 1 more AP doesn't make her deal 0.75 extra damage, it makes her deal 3.75 extra damage (if we assume that all 5 enemies get hit). When Soraka uses Wish, 1 more AP doesn't make her heal 0.7 extra hp, it makes her heal 3.5 extra hp (if we assume that all 5 allies are alive and need healing).

Failing to take the number of affected champions into account means that the formula is meaningless. By not looking at cooldowns, you're getting a sense of how the champion will contribute to a fight that lasts just long enough for them to use each of their abilities once. If you have to make an assumption, that's a fair one. But by not looking at number of affected targets, you're getting a sense of how the champion will contribute to a fight where each of their abilities affects only ONE champion. That's not a fair estimate at all, especially to champs like Sona and Karma that affect multiple targets with all of their abilities.