XII. a) Power Word: Shield formula (3.3.5)
3.3.5 testing shows the shield formula (outside of arenas and battlegrounds) to currently be:
Total Absorb = (base absorb+(0.8068+BT)*SP)*(1+ImpS)*(1+FP+TD)*(1+ICC Aura)
Glyph Heal = (base absorb+(0.8068+BT)*SP)*(1+ImpS+FP)*(1+TD)*0.2*(1+I CC Aura)
Notes
1. No systematic testing of all possible talent combinations and with several levels of spellpower has been done. It is possible that the exact formula as implemented by Blizzard is still slightly different. The results are, however, extremely close with all scenarios tested.
2. The absorb formula isn't exactly the same as the glyph heal formula. The difference is relatively small, so you can use the absorb formula for the glyph heal, too. The computed glyph heal will be a bit too high, then.
3. Currently, as of 2010-05-07, the ICC Aura is always active regarding the absorb formula (even outside of ICC). The glyph heal formula isn't affected, however. Arena and battleground not tested. As the aura continues to increase in strength, expect this bug to be fixed. Even now, 15% additional absorb everywhere is huge. Additional testing has indicated that this effect may not be active between a realm restart and the first time you enter ICC.
Example calculation with 4000 spellpower:
Total Absorb = (base absorb+(0.8068+BT)*SP)*(1+ImpS)*(1+FP+TD)*(1+ICC Aura)
Total Absorb = (2230+(0.8068+0.4)*4000)*(1.15)*(1.09)*(1.15)
Total Absorb = 10173 (8846 without 15% aura effect)