edited to include the later discussion and corrected p-values:
Here are the results after 1002 rolls (batches of 6):
Observed: 420 evades, 248 focus, 334 blanks
Expected: 376 evades, 250 focus, 376 evades
Chi-statistic = 9.87
p-value = 0.00719
......
If we're strictly looking at blanks:
Observed: 668 evades/focus, 334 blanks
Expected: 626 evades/focus, 376 blanks
Chi-statistic = 7.42
p-value = 0.00645
Here are the results from the first 504 rolls (yes, I'm compulsive):
Observed: 204 evades, 137 focus, 163 blanks
Expected: 189 evades, 126 focus, 189 blanks
Chi-Squared Test: this page for reference ( http://www2.lv.psu.edu/jxm57/irp/chisquar.html )
(204-189)^2 / 189 + (137-126)^2 / 126 + (163-189) ^ / 2 = 1.190 + 0.960 + 3.577 = 5.727 so our chi^2 value = 5.727. Generally people use the p < 0.05 value for significance. Our degrees of freedom is 2 (3 possibilities - 1). So using that Table B.2 chart we are between p < 0.10 and p < 0.05. So we're close to it being significant, but we accept that it's in the 'range of acceptable deviation'. There's somewhere between a 10-5% chance of this happening 'by chance alone'. If you roll a few hundred more, it may shift a little.
Conclusion: its close to being able to be rejected as non-fair, but isn't given our picked 5% chance basis for rejecting.
Edit: The 1002 rolls, I get a chi^2 value of 9.85 -- so that puts it p < 0.01 so we can reject that as a fair die.
Yeah that 1000 rolls is way more conclusive.
Those dice are biased with 99% confidence.
I brute-forced the probability distribution at 504 rolls and 1002 rolls, looking at only the evades (counting blanks and focus as a single result).
With 504 rolls, the probability of fair dice rolling at least 204 evades is 9.15%.
With 1002 rolls, the probability of fair dice rolling at least 420 evades is 0.2274%.
This says essentially the same thing as the Chi-Squared test, but stated this way may be slightly more intuitive to understand.
Story time...
Back in December, a bunch of our local players including myself bought third-party dice from the UK. They're the translucent ones with symbols copied from official FFG dice.
They look like the 2014 Regionals dice except for two key differences:
1. No air bubbles
2. Edges and corners are more rounded
It took me 1 attempt to roll this...
My very first game with them, I rolled insanely hot. I didn't think anything of it because that's just how dice work sometimes. My opponent, clearly frustrated by my luck, jokingly says to me
"Your dice were unreal. Are you sure they're not weighted?"
he proceeds to pick up my 6 green dice
rolls 6 evades
That was the first incident that gave me an inkling of a feeling that something was wrong. My thought process at the time was that because they're perfectly translucent and have no air bubbles (inclusions), how could the dice possibly be weighted? So I continued using them for a few months, rolling really well, and brought them out to our local league's playoff match. In that one game, I rolled a ridiculous number of crits - when the video is finally posted, I can post the actual numbers.
Despite paying for them, I shelved the dice after that game. That's just how bad it was. Since December, other players with these dice have noticed the same thing. They roll insanely hot, and blanks are very uncommon. In our group, some players are now asking their opponent to share these dice or not use them at all.
So what makes these dice broken if there are no air bubbles?
It is my opinion that the lack of inclusions is exactly the problem . If you look at the 2016 white Regionals dice, you'll notice that the air bubbles tend to be towards the double-blank area of the die. I've confirmed that in 4 of 6 of my green Regionals dice, there is an increased buoyancy or decreased density specifically in the double-blank corner. I used the salt water test, kept dropping the dice straight down, letting it flip, then repeating until it no longer flipped for consecutive drops.
At first, this was pretty alarming especially since there were whispers that the 2016 Regional dice roll like crap because of all the inclusions (which seem to be much larger than the 2014 Regional dice). So I tested my core set dice too. It turns out 6 of 9 were also weighted towards the double-blank area.
Inclusions tend to be towards the double-blank corner.
So why is that? Well, I think it's because FFG is accounting for the missing material when engraving symbols and is actually trying to balance the dice with inclusions. The faces with engraved symbols on them weigh less due to the material that's missing (although the density is unchanged) relative to the blank faces, especially the double-blank side. That means in order to balance the weight of the faces , you want air bubbles to be towards the blanks.
And that's where the 3rd party dice are flawed. Lack of inclusions on solid dice weights the blanks towards the bottom. I don't know how exactly that works out on the red dice because the blanks are opposite to each other, but the green dice roll like aces for sure. To make matters worse, these dice have rounded edges and corners, making them much more susceptible to flipping.
I'm not accusing these dice of being intentionally weighted. It's just that they don't account for the weight differences due to the engravings.
Please note that these are just my opinions based on my own observations. I play a lot of X-wing, and others have noticed the same thing with these dice - but I can't scientifically prove this beyond my own salt water testing.
TL;DR - if your opponent is using third-party dice without inclusions, I would recommend asking to use his/her dice that game to be safe.
Edited by zerotc