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• Shield Discipline
• Increases the potency of all your damage absorption spells by 20%. Each point of Mastery increases the potency of absorbs by an additional 2.5%.

Shield Discipline is the Discipline priest Mastery, becoming available at level 80. It increases the potency of [Power Word: Shield] and [Divine Aegis].

Shield Discipline increases the potency of the damage absorption 'shields' cast by the priest, significantly improving and encouraging the use of these signature aspects of the Discipline repertoire.

Divine Aegis

[Divine Aegis] is a Tier 5 talent in the Discipline tree. It causes critical heals to create a protective shield on the target, absorbing up to 30% of the amount healed. By increasing the potency of Divine Aegis's protective shields, Shield Discipline potentially improves every healing spell capable of achieving a crit.

[Prayer of Healing] in particular benefits from Shield Discipline, as Divine Aegis is guaranteed to proc from its heals. Prayer of Healing crits proc Divine Aegis twice, granting double the expected benefit. This makes Prayer of Healing the only spell other than [Power Word: Shield] to specifically benefit from Shield Discipline.

As Divine Aegis only procs from critical heals (with the exception of [Prayer of Healing]), Shield Discipline is specifically beneficial to the priest's crits, allowing an increased crit chance to effectively maximise the usefulness of this Mastery, and vice versa. As the only other spell benefiting from Shield Discipline is [Power Word: Shield], the combination of the priest's crit chance and their reliance upon Power Word: Shield (and to a lesser extent Prayer of Healing) will determine the usefulness of this Mastery.

Numbers

Combined with [Divine Aegis], Shield Discipline potentially improves most of the priest's healing repertoire. However the Mastery is of far more benefit to some spells than to others. The numbers below are examples for the purpose of comparing the benefit granted to different spells. However, they reflect only the benefit granted by Shield Discipline, not by Divine Aegis in itself.

With a 13% crit chance, and 3 points spent in [Divine Aegis], 12 points of Mastery provides:

• [Power Word: Shield] with a 30% improvement
• [Prayer of Healing] with a 8.1% improvement
• All other heals capable of achieving a crit with a 1.9% improvement

These numbers illustrate the proportional benefit granted to each type of spell by Shield Discipline, but bear in mind that higher crit chance and larger amounts of Mastery will increase the benefit significantly. In addition, abilities and effects such as [Inner Focus] and [Renewed Hope] can allow certain heals to benefit far more from this Mastery.

While the overall improvement to the majority of the priest's spells may seem small, the improvement to the priest's crits is significant. Following the example above, 12 points of Mastery (with 3 points in [Divine Aegis]) will boost a Discipline priest's healing crits from the usual 200% effectiveness to 278%. This means that a Discipline priest's crits can offer almost twice the benefit of those of a Holy priest, with 12 points of Mastery increasing the spell's output by 178% instead of simply 100%. This makes critical heals (and the priest's crit chance) far more significant for Discipline priests than for Holy priests.

Mastery rating vs critical strike rating

When deciding on secondary stat choices, priests will often have to choose between stats such as mastery rating and critical strike rating. The two stats are generally available in equal amounts, and the rating has the same relative value; around 179 points of mastery rating are required to provide an additional point of Mastery, while 179 points of crit rating provides an additional 1% crit chance. The question is of course the value of each.

Calculating the benefits from increasing these two stats is difficult. In part, this is because of the synergy between the two stats; the more crit chance you have, the more beneficial Mastery becomes, and vice versa. The same increase therefore yields varying benefits, dependent on the current levels of these stats. Also, although the average overall benefits of each stat are closely balanced, the average Discipline priest's crit chance is regularly increased by abilities such as [Renewed Hope] and [Inner Focus]. The combination of these factors means that when stacked in equal proportion, Mastery tends to offer around a 21% larger overall benefit.

However, the question of which stat is more desirable depends on which abilities you wish to improve the most. The ratios vary depending on levels, but on average around 70% of Mastery's benefits go to Power Word: Shield; around 22.5% to Prayer of Healing; and the remaining 7.5% to all other crit-capable heals. Crit rating provides no improvement to Power Word: Shield, giving around 48% benefit to Prayer of Healing, and 52% to all other crit-capable heals.

Players can use their total absorb/heal ratios (obtained via various addons) to see which of these stats more closely matches their playing style. By multiplying the percentages above by the percentages of their total combined absorbs/heals for each of the abilities/ability types, players will be given a number which effectively represents the benefit to their healing over the course of an 'average' healing session. The number for Mastery then needs to be multiplied by 1.21 in order to yield a representation of its benefits. Note that healing from  [Glyph of Power Word: Shield] should be included in both the count for Power Word: Shield and the count for 'crit-capable heals', as it benefits from both. When using this method, do not include Divine Aegis absorbs in either count.

For example, if Power Word: Shield and Glyph of Power Word: Shield account for 35% of your total heals, Prayer of Healing for 5%, and all crit-capable heals (except Prayer of Healing) for 55%, an extra point of Mastery would grant you 36 'points' of benefit, while an extra 1% crit chance would grant you 31. As stated above, these benefits can vary by a few percent depending on crit and Mastery levels; the numbers produced by this method should be roughly accurate.

Of course, the preferred style of play is also a significant factor; priests who rely on particular abilities in emergencies will prefer to strengthen those, and overall success may be determined more by the player's survival in critical moments than on their overall effectiveness. Many factors such as the utility of Power Word: Shield, and the Discipline priest playstyle's reliance upon it, will also sway the decision. Finally, the choice is not too significant to be determined by the enjoyment factor alone. Whether players would rather be able to command powerful heals and unbelievable crits, or summon a constant wall of unbreakable shields, may determine the choice.

Patch changes

• Patch 4.0.3a (2010-11-23): [Power Word: Barrier] has been redesigned, and consequently no longer benefits from Shield Discipline.
  
• Patch 4.0.1 (2010-10-12): Added.
  

External links

• Wowhead
• WoWDB