Drain, Aspir, and Aspir II after the update.

Previous posts have shown that increasing dark magic skill beyond 300 did not increase Drain potency prior to the September 8, 2010 version update, but the version update details state that "maximum values have been increased for certain enhancing magic, dark magic, and blue magic spells whose potency is commensurate with casting skill." The following summarizes the results of checking the potency of Drain, Aspir, and Aspir II without any equipment or other factors that "enhance" any of these spells other than equipment with dark magic skill bonuses.

Raw data is available upon request or I may just post them in the comments below after a week if there is no feedback.

Drain

The distribution of Drain potency (unresisted Drain values) was checked at both 303 dark magic skill (my current dark magic skill level without any equipment) and 340 dark magic skill (with this equipment) on Zvahl Fortalices in Castle Zvahl Baileys (S). The following dot plots show an obvious increase in the maximum value of Drain. Although I was unable to check the distribution of Drain at 300 dark magic skill, it seems that the change in the maximum Drain was done merely by removing the "cap" on increasing it with dark magic skill beyond the 300 level, holding all other potency-increasing factors (maximum-increasing factors) fixed. (In this case, what was fixed was that there were no other factors "present" to affect my results.)



Previously, I gave a formula for the maximum Drain as a function of dark magic skill (without any other potency-affecting factors) as (skill) + 20. The following summary of the minimum and maximum suggests that this formula does not apply beyond 300 skill.

                        ·--------·---------·--------·------------·
                        |    n   |   Min   |   Max  |   Median   |
·-----------------------·--------·---------·--------·------------·
|   Drain (303 skill)   |   60   |   170   |   321  |    247.5   |
|   Drain (340)         |   60   |   173   |   345  |    248.5   |
·-----------------------·--------·---------·--------·------------·

For now, the maximum observed Drain without any other maximum-increasing factors present (or, for shorthand, "naked") is 345.

I do not have access to Drain II so I cannot check it at this time.

Aspir and Aspir II

I actually checked the distributions of Aspir and Aspir II (not omitting resisted values) before that for Drain, and I collected data at both 300 and 302 dark magic skill (on two separate occasions), thinking I had done so only at 300 without realizing later I had skilled up beyond 300. I was lazy and pooled the data, but it is straightforward to see that, similarly to the Drain maximum, the increase in the Aspir (and Aspir II) maximum was done merely by removing the "cap" on increasing it with dark magic skill beyond the 300 level. I checked at 339 dark magic skill with this equipment set. All data collection was done on Stone Eaters in North Gustaberg (S).



I had no idea what the distribution of Aspir II was like compared to Aspir before the update. The previous image shows that, at least after the September 2010 update, the variability of Aspir II (controlling for resist level) is higher than that of Aspir (no reason to assume anything about this beforehand) even though the maximum Aspir II is higher (as expected) as shown in the above image and following summary statistics table:

                            ·--------·---------·--------·------------·
                            |    n   |   Min   |   Max  |   Median   |
·---------------------------·--------·---------·--------·------------·
|   Aspir (300/302 skill)   |   50   |    60   |   120  |     85.0   |
|   Aspir (339)             |   50   |    50   |   135  |     95.5   |
|   Aspir II (300/302)      |   50   |    83   |   180  |    130.5   |
|   Aspir II (339)          |   50   |    56   |   202  |    152.0   |
·---------------------------·--------·---------·--------·------------·

Previously, I gave a formula for the maximum Aspir as a function of dark magic skill (without any other potency-affecting factors) as (skill/3) + 20 (decimals truncated where necessary). The above data shows that this formula does not really apply above 300 dark magic skill. I make no attempt to suggest a formula for the maximum of Aspir II at this time.

The maximum "naked" Aspir observed is 135, and the maximum observed Aspir II is 202.

Summary

Announced in the September 2010 version update, the increase in the maximum Drain, Aspir, and Aspir II values seems to be the result of allowing their potency to increase by increasing dark magic skill beyond 300, holding all other maximum-increasing factors fixed. Before the update, the Drain and Aspir maximum did not increase beyond 300 dark magic skill.

The variability of Aspir II values (controlling for resist level) is higher than that for Aspir values.

I observed a maximum "naked" Drain of 345 (340 dark magic skill), a maximum "naked" Aspir of 135 (339 skill) and maximum "naked" Aspir II of 202 (339 skill). The actual maxima are likely higher and are likely to be attained only by increasing dark magic skill further (well above 340).

Aspir and Drain modeling: an incomplete picture

Earlier, I made some bold statements (at least by my standards) about the distribution of unresisted values of Drain and Aspir. I proposed a model from which I can make explicit, testable predictions.

Specifically, I wanted to see if the model holds at 114 dark magic skill, which can be attained by subbing /DRK on any job without any native dark magic skill (in my case NIN/DRK). Based on the model I described previously, the maximum Aspir without any potency-increasing equipment used is 114/3 + 20 = 58 MP, and the minimum is half that, or 29 MP.

I went out to cast Aspir on Stone Eaters (North Gustaberg (S)) and after the seventh cast I obtained an Aspir of 63 MP, which exceeds the stipulated maximum, so the model doesn't hold for 114 dark magic skill. The following are the observed data values (in order observed):

51 44 56 49 25 51 63 53 35 62 62 46 41 32 44

I then cast Drain on the same Stone Eaters with 246 dark magic skill (NIN75/SCH35 with Dark Arts) and obtained the following results (stem-and-leaf plot):

   6 | 49
   7 | 
   8 | 4
   9 | 
  10 | 
  11 | 
  12 | 
  13 | 4445
  14 | 68
  15 | 044
  16 | 46
  17 | 37
  18 | 9
  19 | 4
  20 | 23789
  21 | 79
  22 | 026
  23 | 55
  24 | 277
  25 | 36
  26 | 01346

(The reason I used Drain and not Aspir was that my scholar is only level 35, and Aspir is accessible at level 36. I would prefer to gather data for Aspir because Aspir values are obviously less variable than Drain values.)

Given 246 dark magic skill, the predicted maximum for Drain is 266 and the predicted unresisted minimum is 133 (both without any potency gear or day/weather effects), so the distribution of Drain (as represented by the sample) seems consistent with the model.

In conclusion, if one were to be technical in describing the scope of the model I proposed earlier, I would say the model is (likely) valid for Drain between 246 and 300 dark magic skill. It is valid for Aspir between 269 and 300 dark magic skill. And, finally, it is valid for Drain II between 285 and 300 dark magic skill. What happens in the 100s is just not that relevant. (In case you are wondering what data I am referring to, you'd have to check my old posts on Drain and Aspir).

Drain and Aspir minimum and maximum

Figuring out things that were already figured out years ago

After reviewing all my posts on Drain and Aspir, I finally realized that I had enough information to specify the minimum and maximum unresisted values, as a function of dark magic skill, for both Drain and Aspir, and since the distribution of unresisted values can be considered approximately uniformly distributed (acknowledging flooring effects), the mean Drain and Aspir can also be specified with reasonable certainty.

Of course, this was something that was figured out years ago. This Drain and Aspir summary page (JP) has some interesting things to say about Vampiric Mitts/Boots, Diabolos's Pole, Y's Scythe, and factors other than equipment, day/weather, and magic burst affecting Drain that do not affect Aspir, but I will leave it to those interested to check out that source while I summarize the the minima and maxima for Drain, Aspir, and Drain II, and speculate on those for Aspir II.

All specified extrema are defined for dark magic skill between 0 and 300, and for clarity's sake, factors that increase Drain or Aspir potency are not included in the statements aside from dark magic skill. It should be understood that any of those other factors increase the maximum and minimum by some multiplicative constant, and these constants can be multiplied in succession (generally, the order of multiplication is first the constant for equipment, then that for day/weather, then that for magic burst, with some twists on Drain potency you can look up yourself) with flooring after each multiplication step to obtain the final values of the maximum and minimum.

Maximum and minimum of Drain

The maximum unresisted Drain is

skill + 20,

and the minimum unresisted Drain is

floor(0.5(skill + 20)).

It follows that the mean unresisted Drain is approximately

0.75(skill + 20).

Currently 320 HP is the highest possible Drain return before any other potency-increasing factors are considered.

Each 1-point increase in dark magic skill (up to 300 total skill) increases the maximum Drain by 1 HP. Other potency-enhancing factors can increase the magnitude of this marginal return.

Maximum and minimum of Aspir

The maximum unresisted Aspir is

floor(skill/3 + 20),

and the minimum unresisted Aspir is

floor(0.5floor(skill/3 + 20)).

It follows that the mean unresisted Aspir is approximately

0.75(skill/3 + 20).

Currently 120 MP is the highest possible Aspir return before any other potency-increasing factors are considered.

Each 3-point increase in dark magic skill (up to 300 total skill) increases the maximum Aspir by 1 MP. Other potency-enhancing factors can increase the magnitude of this marginal return.

Maximum and minimum of Drain II

This discussion of the Hirudinea Earring effect (Hirudinea Earring seems to increase the potency of Drain or Aspir by either 2.5% or 3%) also has Drain II data that is consistent with the following expressions for the minimum and maximum of Drain II.

One thing to note is that Drain II has less variability than Drain I. (A dot plot would help show this.) Another thing to note is that the observed minima seem as though they are based on the expression for the maximum of Drain I. Then the minimum unresisted Drain II is

skill + 20.

The maximum unresisted Drain II is

skill + 85.

The mean unresisted Drain II is

skill + 52.5.

Each 1-point increase in dark magic skill (up to 300 total skill) increases both the minimum and maximum Drain II by 1 HP. Other potency-enhancing factors can increase the magnitude of this marginal return.

Currently 385 HP is the highest possible Drain II return before any other potency-increasing factors are considered.

Note that unlike Drain and Aspir, the variability of Drain II values appears not to vary with dark magic skill. Instead, varying skill merely shifts the distribution of unresisted values to the left or the right.

Minimum and maximum of Aspir II?

While I have yet to see anything regarding Aspir II, I wouldn't be surprised to see the minimum be

floor(skill/3 + 20)

and the maximum be

floor(skill/3 + 85),

but this is subject to verification based on others' experience.

Summary

The following table (image) summarizes the maximum, minimum and (approximate) mean unresisted value of Drain, Aspir, and Aspir II as a function of dark magic skill ("capping" at 300 skill) when no other potency-increasing factors are present.



Other potency-increasing factors increase the minimum and maximum by their corresponding multiplicative constant (e.g. that for equipment), with flooring after each multiplication step.

Increasing Drain potency

This is the last of a series of posts describing my investigation of Drain mechanics, particularly what things increase Drain potency and by how much. The following findings are based yet again on casting Drain on Zvahl Fortalices, details of which (justification, limitations, and whatnot) I described in previous posts (but weren't that detailed).

The motivation: Excelsis Ring

Having received the Excelsis Ring from the Bastok sequence of Wings of the Goddess nation-oriented quests, I wondered whether this ring actually increased the potency of Drain, which should be understood as increasing the maximum Drain or the average (mean) Drain value.

Having previously shown that Drain potency could possibly "cap" at 300 dark magic skill holding all other relevant factors fixed, I felt that it would be useful to verify, in the process of determining whether Excelsis Ring actually increases Drain potency, that Drain potency doesn't increase at higher levels of skill (again), specifically 331 dark magic skill.

After establishing two baseline samples at 331 dark magic skill given no other potency-enhancing equipment (or day/weather effects), I then obtained a sample adding Excelsis Ring to the "baseline." After that, I figured it would be helpful also to quantify the effects of Pluto's Staff and Dark weather on Drain potency, both relative to the baseline.

Wait a second... aren't you ever going to describe an experimental procedure in more detail?

I could, but seriously, is it that hard to think of equipment swaps that guarantee your current HP is 350-400 HP lower than your maximum HP? Hint: HP-increasing equipment upon Drain casting counts. Also, it isn't that hard to think of ways 331 dark magic skill can be attained. I could take a screenshot of the equipment used, but that would mean logging into the game.

Results

The above image is yet another set of dot plots providing a visual summary of the five samples obtained. In the past, I made no statements about the actual distribution of Drain (controlling for resist level), but by now it should be pretty obvious that a uniform distribution is a good model for the data, so further insights will be based on this model.

Also, there were a few Drain resists observed, but as they are obviously resists they can be ignored for the purposes of potency estimation, and the vertical lines denote the suspected minimum (160 HP) and maximum HP (320 HP) drained for the control samples, to be discussed later. A table (ASCII, yes I am that lazy) summarizing the extrema and median of the unresisted Drain values for each sample follows:

                    ·--------·-------------·-------------·------------·
                    |    n   |   Minimum   |   Maximum   |   Median   |
·-------------------·--------·-------------·-------------·------------·
|   Baseline 1      |   48   |       162   |       305   |    223.0   |
|   Baseline 2      |   50   |       160   |       319   |    238.0   |
|   Excelsis Ring   |   51   |       171   |       336   |    255.0   |
|   Pluto's Staff   |   61   |       184   |       365   |    263.0   |
|   Dark weather    |   30   |       190   |       349   |    288.5   |
·-------------------·--------·-------------·-------------·------------·

Speculating on what the extrema could tell us, it looks as though the variability of the data (as indicated by the range of observed values) is highest for Pluto's Staff, which is consistent with the idea that Pluto's Staff increases potency by some multiplicative factor. Also of interest is the possibility that the minimum is merely half of the maximum, so the observed minima could provide some insight on what the maxima should be.

Another obvious thing to note is that even at 331 dark magic skill, there is still no evidence that Drain potency is higher compared to that at 300 skill, so it is reasonable to conclude, considering all the data to date, that the Drain "cap" (holding other potency-enhancing factors fixed) seems to be met somewhere near 300 dark magic skill (if not exactly at 300). Technically, I could invoke an equivalence test yet again (as I did in a previous post), but you would have to be a tool to demand one here.

Since we know that a Pluto's Staff and single Dark weather each increase direct-damage magic (as shown by changes to the initial damage of any of the Bio spells, allowing for truncation) by 15% and 10% respectively, it wouldn't be surprising if these factors increased Drain potency by the same amount. It stands to reason that Excelsis Ring could behave in the same way (but increasing potency by a lesser amount).

One way to estimate the mutiplicative factors is to divide the observed maximum Drain for each of the non-baseline samples by the observed maximum for the baseline samples combined.

Excelsis Ring appears to increase Drain potency by a percentage near (336/319 - 1)100% = 5.3%. But I suspect the maximum Drain for the baseline is 320 (I just wasn't lucky enough to observe it), which would mean the increase in Drain potency from Excelsis Ring could be 5%.

Keeping in mind that the maximum Drain for the baseline could be 320, then Pluto's Staff appears to increase Drain potency by 15%, and Dark weather appears to increase Drain potency by 10%, and these figures are consistent with their effects on direct-damage magic.

An alternative, more statistical method of potency estimation is to divide the mean Drain value for each non-baseline sample by the mean Drain value of the pooled baseline sample. The ratio is then an estimate of the multiplicative factor for the potency-increasing equipment of interest. From the basic bootstrap, a set of simultaneous 95% confidence intervals for the ratios of the means can be obtained.

                    ·----------------·-------------------------------·
                    |   Mean ratio   |   Confidence interval (95%)   |
·-------------------·----------------·-------------------------------·
|   Excelsis Ring   |     1.088056   |        (0.996482, 1.183355)   |
|   Pluto's Staff   |     1.144933   |        (1.057611, 1.237342)   |
|   Dark weather    |     1.193882   |        (1.085225, 1.303625)   |
·-------------------·----------------·-------------------------------·

(Edit: 07/24/2010. I realized the bootstrapped data also included Drain resists. Not correct to include them in the data. Estimates have been corrected.) Not surprisingly, statistical significance for the potency effect of Excelsis Ring isn't achieved, but this is merely a consequence of the sample size. The effects of Pluto's Staff and Dark weather are large enough to yield statistical significance.

Conclusion and open issues

Excelsis Ring appears to increase the potency of Drain by 5%. Pluto's Staff was verified to increase the potency of Drain by 15%, and single Dark weather was verified to increase the potency of Drain by 10%.

Now, this still leaves the accuracy effect of Excelsis Ring to be determined, but quantifying it is difficult as it likely does not impart a large accuracy bonus (if there is one at all). If I were to do so, I'd be interested in determining whether Dark weather or Darksday has an effect on Drain accuracy. If so, it wouldn't be unreasonable to generalize to other types of magic and conclude that the weather or day can affect magic accuracy in general.

Regarding the mechanics of Drain in particular, it seems that the distribution of Drain could be uniform (discrete or continuous with truncation, it doesn't really matter) and that it is parameterized only by the maximum, with the minimum possibly being exactly one-half the maximum. Provided that this holds, one obvious implication is that the variability of Drain increases with dark magic skill (up to a point), and that it also increases with other various potency factors present. Taken altogether, these factors can make it very difficult to draw any conclusions about Drain (and Aspir by analogy) based on eyeballing alone.

As far as the distribution of Drain values given some sort of resist, it still isn't clear how resists relate to non-resists, but resists aren't that interesting to me so I would never willingly investigate Drain resists.

Finally, why have I never made any explicit claims about what the actual value of the Drain cap should be? Considering that Zvahl Fortalices take increased magic damage, it's possible that they also take increased Drain damage, and 320 might not be the "true" cap given that no other potency-enhancing factors are in play. But I was interested in differences, not actual amounts.

Does Drain have a cap?

This is a continuation of a line of inquiry regarding the mechanics of Drain, specifically whether an "unconditional" maximum value of Drain exists (still thinking statistically...) and, if so, whether it can be achieved with a minimum level of dark magic skill such that additional skill does nothing to increase the unconditional maximum (holding all other relevant factors fixed, obviously).

To put it another way, does additional skill do nothing to increase Drain potency?

First, I supposed that a maximum Drain value could be achieved with a minimum dark magic skill of 300 (or somewhere around 300), and that 25 additional skill would therefore not change the average potency of Drain. Data were collected in the usual manner (taking care not to cast Drain with Dark weather in effect; see previous posts for more details on "experimental procedure"). All other factors affecting potency and or accuracy were held fixed for both samples. I obtained the following results:

The maximum Drain observed given 300 dark skill was 319 and the maximum observed given 325 dark skill was 318. Also note that there were more "obvious" resists under 300 skill than under 325.

Considering the data as a whole, does 25 additional dark magic skill really have no effect on Drain potency? Noting the lack of difference in maximum Drain values should be enough for most (and it is for me), but let us also consider a way to apply statistics.

First, we can treat this data as though we were doing equivalence testing, so we need to decide what average difference would be considered a sign that there is a difference in Drain potency.

Recall that last time, I observed that, given 269 dark magic skill, I observed a maximum Drain of 288. Here, I observed a maximum Drain of 319 given 300 dark magic skill. Does one point of additional skill really increase the maximum (and minimum) Drain by 1 HP? Who knows, but suppose it were the case. Then 25 additional skill would have increased the maximum (and average) Drain by 25 HP. Let us then consider any observed difference in averages between 0 and 25 to be the result of chance, provided that there really is no difference in potency. Of course, there are some observations that are obviously resists, so let us also use the crude cutoff that any values below 150 be excluded from the analysis.

By the logic of an equivalence test ("two one-sided tests"), a 90% confidence interval for the difference in average potency between 325 skill and 300 skill is (-7.003157, 19.665328). This confidence interval is completely contained in the interval [-25, 25], so from the standpoint of statistical significance one can say that 325 skill is equivalent to 300 skill as far as average potency is concerned.

Conclusions

There appears to be no difference in Drain potency between 300 dark magic skill and 325 dark magic skill, holding all other relevant factors fixed. Additional dark magic skill still appears to affect Drain accuracy beyond 300 dark magic skill, however. Drain potency could cap at 300 dark magic skill (holding other factors fixed).

Personally, these findings devalue somewhat my dark skill equipment that is devoted solely to Drain or Aspir, of which there are three pieces. Certain pieces such as Sorcerer's gloves and Wizard's tonban still provide large boosts to accuracy (at least it is expected).

INT affecting Drain accuracy, continued

This is a followup to an earlier post showing that INT affects the accuracy of Drain.

Having found a way to suppress my base INT even further, I increased the difference between the two INT "treatments" to 60 (54 INT and 114 INT). As the resist rate for 121 INT could have been floored (presumably at 5%), maybe a 7-INT decrease would result in some increase in resist rate. The following dot plots summarize the distribution of the observed data visually:


The criterion I used last time to determine a difference between two cases, the number of Drain values set "far enough" apart from the bulk of the data (over the total number of samples in each case), doesn't quite work this time, in part because it is kind of difficult to define the "bulk" of the data for the 54-INT case. (It appears that there are more resists in general by an alternative criterion of number of Drain values below 144, though, and more for the 54-INT case than the 114-INT case.)

Instead, I probably am better off relying on the two-sample t-test to demonstrate statistical significance. The sample means for 54 INT and 114 INT are 154.28 and 191.33, respectively, and the 95% confidence interval for the difference of means is (12.213, 61.898), so the evidence, taken together (including that in the last post), provides strong support for the contention that INT affects Drain accuracy (provided that all the assumptions I stated last time hold, and why wouldn't they?), specifically that increasing INT increases its accuracy (in the form of fewer resists).

The most obvious practical implications of this finding is that the "conventional wisdom" that holds prioritizing dark skill above magic accuracy above recast reduction for Drain (and Aspir by close analogy) should incorporate INT, arguably before recast reduction. Where the benefit of reducing recast timers for Drain and Aspir is not fully realized (more often than you think) and the resist rate is suspect, the opportunity cost of recast reduction is usually additional INT, and it might not be a cost worth incurring depending on the actual trade-off.

Does INT affect Drain accuracy?

(Correction: 06/18/2010. I meant /SCH instead of /DRK toward the end. I've gone mental...)

A while ago, I asserted that INT "seems likely" to affect the accuracy of Aspir and, by implied analogy, Drain, but I had absolutely nothing on which to base this assertion. Not quite as baseless is assuming that, since then, there has been absolutely no evidence presented anywhere to support or refute that assertion.

Some problems with getting data to show whether INT affects Drain accuracy

Why do I assume that? I'm not trying to be hater and talk shit, as ignorance about this is not on the level of, say, ignorance about the party-based, hidden latent effects of curry food items.

At least where examining the effect of INT on Drain accuracy is concerned, one problem is that if you're in a situation where you have good reason to believe Drain accuracy isn't "capped," you wouldn't want your HP to be low enough to allow you obtain the actual quantity of HP taken with Drain. (Low-level beetles and worms are not acceptable targets for examining Drain accuracy with level 75 jobs, and EM+ worms are not easily accessible... yet.)

Another problem, related to the first, is that the distribution of Drain still isn't known today, and "censored" values of HP drained don't help to provide insight into that. ("Censoring" is one way to describe the fact that Drain values reported in chat logs are based on maximum HP; any HP restored beyond your maximum HP does not count in the final chat log figure, so at best you only know at least how much you drained, not its actual value or whether your Drain was resisted.)

These are some of the problems that hamper data collection.

A way to avoid these problems?

If only there were a stationary target that didn't fight back, that could allow you to suppress your HP safely, for which Drain accuracy has the possibility not to be capped at level 75, and for which you could gather Drain data without interference from other players...

Zvahl Fortalices definitely satisfy the first condition, as they do not move. They also satisfy the second condition, as two of the fortalices deeper into Castle Zvahl Baileys (S) do not have any mobs wandering nearby, including Dark and Ice Elementals. Zvahl Fortalices definitely seemed like a promising candidate for Drain testing, so I actually set out to get some data to determine if INT has some accuracy effect.

That left the third and fourth conditions. Of course, I had no idea if it would even be possible for Drain accuracy not to be capped, but that would be part of the data collection anyway, with the hope that my Drain accuracy could be decreased enough to raise the corresponding resist rate above the (assumed) 5% resist rate floor. As for people doing skill-ups, I don't really begrudge them trying to maximize their skill-up opportunities, as this method of skill-up is liable to be "nerfed" come the June 21 version update.

Goals of data collection, some assumptions, and results

My way of determining whether INT has an effect on Drain accuracy is based on a simple two-sample comparison of the occurrence of resists, one sample based on "low" INT (71 in my case), and the other based on "high" INT (121). Again, this was based on the hope that my resist rate would not be floored (at 5%) for the low-INT case. This, in turn, is based on the assumption that the resist rate is floored at 5% and rises with decreasing magic accuracy. If the data shows the resist rate being above 5% for low INT, I conclude my Drain accuracy isn't capped for low INT. (That alone would not show that INT has an effect on accuracy; I would need the second sample under high INT as well.)

But what is considered a resist? Similar to the Aspir data collection I cited previously, it would be necessary to get some sense of the distribution of unresisted Drain values, with any low Drain values set "far enough" apart from the bulk of the data considered occurrences of a resist. This is the main assumption concerning the interpretation of the data (but a reasonable one).

Now, what about the other assumptions? I merely state some of them here because I simply was not interested in testing them, and I didn't collect enough data to test these assumptions anyway.

• No differences among Zvahl Fortalices that could affect the results. This is a catch-all assumption concerning possible differences in magic evasion, INT, etc., but I don't think they exist (otherwise, fuck you, SE). If it could be shown that two Fortalices have two different base INT values (even if only a +1 INT difference), you would have to wonder about other possible confounders like level difference as well (can't assume these are level 75, etc.).
• Even if there is a bonus to Drain on Fortalices, similar to a MAB bonus for elemental magic, it should still be possible to tell the difference between a resist and a non-resist. Bio II initial damage shows there is a MAB bonus, but even if there is a similar bonus for Drain (not MAB-related, of course), it shouldn't affect one's ability to distinguish between resists and non-resists.
  
• The equipment bonuses (or penalties) aside from +50 INT for the "high INT" case have no effect on the accuracy of Drain. Now, obviously, I didn't put on equipment with dark magic skill or magic accuracy (or use a Dark Staff or Pluto's Staff), leaving only base attribute bonuses and penalties. Now, if you think MND and CHR actually have an effect on Drain accuracy, I'd like to hear the justification. If there are hidden accuracy effects on my equipment, that could be a problem, though.
  
• Dark weather and Darksday have no effect on the accuracy of Drain. This is not really an assumption, as I didn't collect any data during Darksday or under Dark weather, but I just mention it anyway as they are potential confounders.
  

Now, the results. First, dot plots of the results as an initial visual impression, under low INT (top dot plot) and under high INT (below), suggest a minimum and maximum non-resisted Drain given 269 dark magic skill:


Before jumping into a discussion of the maximum and minimum Drain values, based solely on the criterion of a resist I described earlier (low values of Drain set "far enough" apart from the bulk of the data), there are 10/65 resists under low INT and 2/63 under high INT, so this data appears to provide good evidence that increasing INT increases the accuracy of Drain, especially if you think that for the 121-INT case, the resist rate was floored at 5%. I see no reason to be pedantic and report a confidence interval or p-value.

Under both low INT and high INT, the Drain maximum (unresisted) was 288 under 269 dark magic skill. It has been said that the maximum Drain and Aspir are 300 and 100, respectively, without any potency-enhancing gear (anecdotal discussion on BG), so if it can be shown that the Drain maximum is 288 under 269 skill for other mobs, you have to wonder how Drain potency actually scales with dark magic skill.

The location of the unresisted Drain minimum is less straightforward. One possibility is that it could be at 144 HP, which would be exactly half of the unresisted Drain maximum. It would be interesting if this relationship between maximum and minimum actually holds for all levels of dark magic skill (with other potency-enhancing factors presumably serving only to affect scale). One way to check this would be with with /SCH as a subjob.

And what of the relationship between the HP value of a resist and a non-resist? I actually got 29 HP under the low-INT case, and it's difficult to describe this relationship with with small samples. But small samples are enough to reach the major conclusions.

Conclusions

Based on the criterion that low values of Drain set "far enough" apart from the bulk of the observed data should be considered resists, additional INT appears to increase the accuracy of Drain. Ideally, the data collection should be repeated in an attempt to replicate this result.

Data collection could be performed using /SCH as a subjob. +50 INT (if it could be achieved) should still be able to manifest in the form of increased accuracy (provided INT does have effect), and further exploration of the relationship between dark magic skill and unresisted Drain maximum could be done, along with that between (unresisted) Drain maximum and minimum.