Let's talk about snatch

[Inb4whales]

I've done plenty of runs using D'art equipped with 2nd lvl Snatch from Gran as an extra ability (Especially for the Advent battles).

What I noticed generally is that while the number of chests increases noticeably on any characters that you killed with Snatch on them, the number of gold (not sure about platinum) chests significantly decreases.

This was most noticed back when I was doing the Apocalypse and Phoenix events where using snatch on mobs as well as the boss allowed me to obtain 2 pages worth of drops, even though the frequency of dropping gold chests noticeably decrease as well.
Anything above the Snatch level of 5 on the enemy started decreasing my gold drop rates all the way down from 0 to 1, while if I don't use Snatch, I would consistently get around 1-2 per run.

This raises the question, how does this "Item drop rate" increase works?
Does it simply increase the drop rate of the bronze and silver chests thus causing the drop rates of gold to significantly decrease?
Or is it something else? If so, is it even worth using Snatch at all in these new buffed up drop rate Advents?

[sanahtlig]

I proposed a study design here (http://harem-battle.club/kamihime-project/3003-advent-event-eidolon-world-advent-battle-vs-apocalypse-21.html#post63965). You can spearhead it if you're interested in data collection. At this point, I'd recommend logging gold chests or silver chests rather than a specific drop of interest. However, you might have difficulty finding people who'd sub out a useful ability for Snatch and run Ultimate for you.

[Skulkraken]

How many total Snatch/Snatch-less Ultimate runs would need to be logged in order to be statistically relevant?

[sanahtlig]

How many total Snatch/Snatch-less Ultimate runs would need to be logged in order to be statistically relevant?
Assuming a 5% drop rate increase, we'd need about 100 chests of a given rarity in each Snatch group (Snatch, no Snatch). To observe a smaller effect, we'd need more.
Sample size calculator (https://www.statisticalsolutions.net/pssZtest_calc.php)

Ideally, you'd then want to repeat that a few times. That's why I recommended pooling data from multiple users.

[Skulkraken]

...I see.

Wouldn't it be fine to start with just copper chests, then? Ultimate always drops 20+ of them, so it should be feasible even for one player to collect enough of them to do an analysis in just 5 or so runs...or am I misunderstanding what you said?

[sanahtlig]

...I see.

Wouldn't it be fine to start with just copper chests, then? Ultimate always drops 20+ of them, so it should be feasible even for one player to collect enough of them to do an analysis in just 5 or so runs...or am I misunderstanding what you said?
Copper chests are a good place to start. But since they drop from trash mobs, that complicates the experiment. You'll have to make sure you land X stacks of Snatch average on each mob (and a minimum of X stacks on the boss). My initial power estimate assumed 5 stacks. We can lower that number, but then you'll have to collect more chests (e.g., 300 for 3 stacks, 700 for 2 stacks). Meanwhile, the control group will do all runs without Snatch. For each group, record the number of chests of each rarity that drop in each run (just record the final tally the game gives you before you hit the next button) until a total of 100 chests of the rarity of interest are collected (more if less than 5 stacks of Snatch per mob). We can then do a t-test on the series of drops per run in each group.

As long as each person uses the same methodology, numbers can be pooled to achieve these targets.

[Skulkraken]

Alright, then. I'll give it a go a little bit later. Whales, can you log your Snatch runs? I'll log some no-Snatch runs for use as the control group.

[sanahtlig]

Now that I have some pilot data, I can give more exact sample number requirements. Here's the number of runs required to spot a difference in bronze chests assuming X stacks of Snatch per mob on average (minimum X stacks on boss). This assumes an effect of Snatch of at least 1% per stack.
5 stacks (5% difference): 5
3 stacks (3% difference): 12
2 stacks (2% difference): 27
1 stack (1% difference): 105

I currently have 13 control runs recorded (no Snatch).

- - - Updated - - -

My Snatch data is available in my Kamihime Project spreadsheet (https://docs.google.com/spreadsheets/d/1PhfOAQk6EyK5l33ux_C4T-cexVIQp6D-_Hbd-OO1OmQ/edit#gid=1844069485) on the Snatch tab. I reached my quota for the event and will likely not be running much more. Do note that if the Snatch group data isn't populated before the end of the event, the opportunity to use this data for statistical analysis will be lost. Intriguingly, my first run using Snatch gave me more bronze chests of the 13 runs without, and matched the maximum of silver chests from those runs, suggesting a readily observable effect. The run also took like 50% longer...

[Skulkraken]

Okay, 100 (give or take) copper chests:

Run 1 - 21 copper, 5 silver, 3 gold
Run 2 - 24 c, 5 s, 3 g
Run 3 - 21 c, 6 s, 3 g
Run 4 - 18 c, 5 s, 3 g
Run 5 - 23 c, 5 s, 3 g

[sanahtlig]

While no one else contributed any Snatch runs to make this a more robust result, even with a sample size of 3 in the Snatch group there's a clear effect that's statistically significant. Applying 2-3 stacks to each trash mob and 5 or so to the boss currently results in a drop rate increase of bronze chests of about 10%. This likely applies across the board to all rarities. My guess is that Snatch currently boosts drop rates by about 3% per stack, though that's unverified.

Supposedly Snatch was nerfed at some point in the JP version. This nerf may not yet be applied in our version.