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.