Crowd control duration

Crowd control is built exactly like ability damage: the same per-item multiplier, a different growth rate, and one global cut at the end.

duration = base × abilityPower / 100 × ccProgression^(itemPower / 100) × 0.7

@ccpowerprogression is 1.0474 for one-handed weapons and 1.0564 for everything else, against 1.0918 for damage: crowd control grows more slowly than the damage on the same weapon. The final 0.7 is @ccdurationfactorplayers, and it is the reason a tooltip’s duration is shorter than the number in the files.

Against mobs

There is no second factor. Where an ability behaves differently against mobs, the files hold two separate entries with their own bases (Arcane Orb’s silence stores 1.68 for players and 3.36 for mobs), and both go through the same arithmetic.

What counts as crowd control

The nodes that are crowd control by definition: stun, root, silence, pull, knockback, forced movement and cannot-attack. An entry flagged @ignorecrowdcontrolresistance keeps a fixed duration instead.

Worked example

Spirit of Vengeance, root base 4.43, off a Harvester Garb (ability power 100, chest):

at 700 IP:   4.43 × 1.00 × 1.0564^7  × 0.7  = 4.55 s
at 1100 IP:  4.43 × 1.00 × 1.0564^11 × 0.7  = 5.67 s

Arcane Orb, silence base 1.68, off an Arcane Staff (ability power 120, one-handed):

at 700 IP:   1.68 × 1.20 × 1.0474^7  × 0.7  = 1.95 s
at 1100 IP:  1.68 × 1.20 × 1.0474^11 × 0.7  = 2.35 s

The second example is the one that pins the ability power multiplier. On armor it equals 1.0 and is invisible; only a weapon carrying 120 reveals it.

Verified

Both examples above, at both item powers, against in-game tooltips, including the mob variants, which come out at exactly double.