Shaman · Restoration · tier 3 · from level 20

Ancestral Healing

Rank 3/3

Increases your target's armor value by 25% for 15 sec after getting a critical effect from one of your healing spells.

Doesn't change the damage or healing of any Shaman spell.

Averages, counting crits and misses, for a level 60 Shaman with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.