Guides - Shield versus Defense

WARNING MATH !!!

NOTE: This post has been supplemented by: http://www.tankingtor.com/2012/07/swtor-optimal-tanking-gear-guide.html which describes optimal gearing for a tank in more detail and with more real game examples.

For the last few days I've been theorycrafting with Shield chance/absorb and Defense rating to see how the survive-ability works out and with diminishing returns where you're better off spending those points.

For the sake of these calculations both defense and shield proc off the same types of attacks.  They do not proc off all attacks (I'll be writing up a guide for this later) but they do proc off the same attacks so weighting them based on what they effect has no bearing on calculations.

Because of the types of damage they defend against both stats are inherently more useful in PvE than in PvP, but there is no difference between them for how effective they are in either place.  IE: They are both equally effective in PvE and equally ineffective in PvP.

So - premise:
Most of my numbers are based off the Jedi Guardian base defense and shield chances.  Some of my specific numbers will change based off your spec - the actual impact and overall guidelines will be the same no matter what your final numbers are.

For example:  Adding 5% shield change costs ~90 attribute points.  For a JG that will bring my total to 25% shield chance (base 20), for someone else it will bring them to 10% (base 5), or 20% (base 15).  The actual bonus calculation from skill points doesn't change based on what your base is.

Here is the diminishing returns chart for Defense and Shield.

You'll see the chart starts at 20% shield and 5% defense, that's just because that's where my guardian starts.  The chart doesn't alter based on your baseline other than the starting point moves up or down.  So if you have base 0% shield your max will be ~50% instead of ~70% shown.

The bottom is how many skill points it takes to reach that value.  You can see why reaching 50% absorb OR shield requires you to sacrifice in many other areas.

The next graph shows how much return you get for your point value.  You'll see at the beginning that Absorb gives the largest increase per point spent, then slowly falls below shield rating coming more even with Defense rating.

This graph led me to ask the question, How much value does each percentage increase actually net you.  IE: Is it better to stack Absorb for the higher net gain at the start or does Defense provide more mitigation even with a lower value.

Bring on the math!!

First I set up my experiment.
Based on 100 hits doing 100 damage, what is the mitigation gained for each stat.
NOTE: I altered this primary experment in various ways throughout my calculations (1000 hits of 100 damage, or 100 hits of 1000 damage) and it had no effect on the actual 'winners' in the formulas.  The only difference was how much damage was actually mitigated.

Defense was quite linear since I was working with round numbers, 5% defense rating dodges 5 our of 100 attacks - effectively netting 500 damage mitigation.  Easy.

Where things got complicated was with the Shielding formula.  It wasn't good enough to calculate how much gain you got from one stat or the other because they were dependent on each other.  So, to find the sweet spot (best investment for points spent) I set up a matrix of Shield v/s Absorb.  I'm attaching a screenshot for you just so you can see what I was working with.  This is just a small sample of the first series, my chart actually went to 2450 points spent on either talent (~5000 total points spent) just for the sake of correctness.

Using the above chart I determined the best distribution of skill points for absorption and shield rating to get the highest mitigated damage value.

My findings are:
Until you spent 120 points directly in absorption shield gives less of a benefit.
Sweet spot at ~300 total points spent (180 absorption, 120 shield rating)
Sweet spot at ~400 total points spent (230 absorption, 170 shield rating)
Sweet spot at ~500 total points spent (270 absorption, 230 shield rating)

You see the trend, shield rating slowly catches up to absorption rating in terms of effectiveness.
At approximately 680 total points spent shield and absorption should be at a 1:1 ratio.  From here Shield becomes more effective then absorption, so you should stack 10 points of shield for every 8 points of absorption (this ratio is a pure approximation, in fact at 690 total points the ratio is 0.98:1, then at 690 points  it is 0.96:1, then at 700 points it is 0.95:1)

People have asked for Ratios and why they don't match my exact sweet spots, that's because every 10 points you put into shield rating the ratio changes on an exponential curve.  The best I can do is give you a head start with the below image.  Actual Shield and Actual Absorb are the ratings on your tooltips given by the skills you've chosen.  Add these numbers to your base chance for a total number.  So for my JG I add 20 to all numbers to get my actual tooltip total.

Shield Points and Absorb points are the actual amount of points put into the skill to get the outcome percentage.

For completeness sake at ~1590 points total you should have: 710 absorption, 880 shield rating.  You see here how Shield rating gradually overtakes Absorption and then surpasses it.

See chart below for trend lines.  It is jerky because I am counting x,y points in multiples of 10, so it isn't a perfect formula.  If I was doing it in single points used it would be much smoother and take much more time to compile.  The rough numbers I'm giving you should be close enough for your needs.  There isn't any way you'll be getting +1 shield anyway, it'll probably be +25 (minimum) so everything else is just superfluous.

You see the initial spike in Absorb usefulness over Shield usefulness.  After that it rapidly declines until almost coming even, then slowly Shield overtakes Absorb for usefulness.

This chart only goes up to 730 total points spent because I got tired of putting in key points, assume the trend continues so that at ~1590 points the graph line would be at 0.8 (very slowly declining toward the X axis).

What does it all mean?

So, now with a "sweet spot" for shield and absorb usage we can determine if it is more effective to spend 10 points on Defense rating, or 10 points (mixed between shield and absorb to provide optimal performance).

Here are my findings:

	Defence		Shield
Points	Mit Dmg/Points		Mit Dmg/Points
10	53.67565		42.21974
20	28.65313		22.1951
30	20.29746		15.50416
40	16.10865		12.14692
50	13.58668		10.12336
60	11.89822		8.76681
70	10.68613		7.791556
80	9.771831		7.054732
90	9.056122		6.476969
100	8.479474		6.010641
110	8.004007		5.62544
120	7.604467		5.631648
130	7.263369		4.604626
140	6.968226		4.830733
150	6.709877		4.508684
160	6.481454		4.465422
170	6.277701		4.202751
180	6.094534		4.18327
190	5.928726		4.064324
200	5.777695		3.956067
210	5.639351		3.767682
220	5.511984		3.687722
230	5.394181		3.698407
240	5.284764		3.544307
250	5.182744		3.56076
260	5.087283		3.423808
270	4.997668		3.444199
280	4.913286		3.392012
290	4.833611		3.275046
300	4.758184		3.299423
310	4.686608		3.19299
320	4.618533		3.218745
330	4.553652		3.121207
340	4.491695		3.14779
350	4.432422		3.115059
360	4.375619		3.028529
370	4.321096		3.055917
380	4.268682		2.975498
390	4.218225		3.002871
400	4.169585		2.927799
410	4.122639		2.954971
420	4.077274		2.932411
430	4.033387		2.864216
440	3.990885		2.891071
450	3.949683		2.826825
460	3.909703		2.853178
470	3.870874		2.792472
480	3.833131		2.818258
490	3.796414		2.801578
500	3.760666		2.745546
510	3.725838		2.770603
520	3.691883		2.717322
530	3.658755		2.741712
540	3.626415		2.69094
550	3.594825		2.714647
560	3.563949		2.701608
570	3.533757		2.654211
580	3.504216		2.677054
590	3.475298		2.631681
600	3.446977		2.653822
610	3.419228		2.642455
620	3.392027		2.599835
630	3.365353		2.621092
640	3.339185		2.580137
650	3.313503		2.6007
660	3.28829		2.59059
670	3.263527		2.551924
680	3.239199		2.571615
690	3.215291		2.534345
700	3.191788		2.553364
710	3.168675		2.517401
720	3.145941		2.535764
730	3.123573		2.527056
740	3.101558		2.492906
750	3.079887		2.510443
760	3.058548		3.225495

The actual values are meaningless.  What you are looking for here, is the larger value is more useful than the smaller value.

Reading the above table:
Points refers to how many points spent in the talent.
As you can see spending a small amount of points nets a large increase at very low ranks.  Spending at least 40 points on defense and at least 30 points in the shield (less than 120 points so 0 shield and 30 absorb based on previous calculation) nets you huge gains in survive-ability.

Using the above numbers you can easily see where putting points will net you the most survive-ability.  For example, upon reaching 400 points on defense (4.1 usefulness) you should have also spent 190 points into the shield (at optimal distribution this is ~130 absorb and ~60 shield) also 4.1 usefulness.

From that point Defense almost equals shield for a 1:1 point distribution, only slightly favoring Defense.  The trend continues all the way up the point spread, with defense being more useful then shield.

NOTE: As Defense increases the "weight" of shielding stats decreases.  This happens because you will be dodging more attacks, and therefore will see less effect from your overall shield mitigation.  This doesn't mean that your shield is less effective, but you will see less mitigation coming directly from it - which will tend to skew numbers at higher levels.  None of the math here takes that fact in to account since I was only comparing direct mitigation values and not adding the mitigation effect together into an overall formula.

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Everything I've said also has a caveat.  This is overall AVERAGE survive-ability.  Fighting a boss that throws lightning at you that you can't block or dodge but you can shield makes defense useless.  This doesn't happen very often, usually anything that you can't block or dodge you also can't shield.


TL;DR Recap:

• Spend 120 points in absorption before stacking shield rating
• After 120 points see table screenshot for optimal distribution
• Put at least 40 points toward shield and defense to start, ignoring either causes a huge hit in survivability
• Defense is more useful then shield for overall mitigation, stack 2 points of defense : 1 point of shield (split shield optimally between absorption and shield chance according to above calculation)
• At ~400 defense and ~200 shield start stacking at appromxately 1.1 defense : 1 shield ratio

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