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 Post subject: VASSAL Dice
PostPosted: Thu Jun 21, 2012 9:39 am 
Death Star Designers
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If you've played on VASSAL, you've experienced "bad dice". You get a streak of bad rolls, or your opponent gets a streak of good rolls. Either way, somehow the VASSAL RNG (Random Number Generator) is against you.

Then again, if you've played minis ever, you've probably experienced "bad dice". It happens in real life, too. It happened to me just this past weekend, when I played 2 games in a row where nearly big roll went my opponent's way (big crits or inits for him, big misses for me). Still though, it seems like it's worse on VASSAL, doesn't it?

I've been tossing around the idea of doing a rigorous test of the VASSAL RNG, and looked further into doing it this morning. Unfortunately I ran into a few roadblocks. It took me a while to find what I THINK is the actual RNG method in the VASSAL source code, then I couldn't find a good RNG tester that would work on my work computer. But what I did find is some interesting discussion on the matter.

First I read that VASSAL used the basic Java .rand() method for the RNG. This is an alright way to do it, but that method has been criticized enough that it could cause some streaks. But wait, the VASSAL guys knew that, too, so they created an updated method using a Mersenne twister. You can read more about the Mersenne twister here: http://en.wikipedia.org/wiki/Mersenne_twister, but suffice it to say that it's a pretty solid RNG and definitely good enough for games like SWM.

Then I also found this pretty good analysis of VASSAL dice, using d6s: http://www.chad-libra.lunarpages.com/~v ... l/RNG.html. That page isn't dated, so I don't know if it was created when VASSAL was using .rand() or if it was created when they were using the Mersenne twister method, but it's an interesting analysis. Since most people complain about streaks, the "correlation between rolls" part is most interesting, and had a sample size of 85,450. It produced a very significant result showing that one roll is basically independent of prior rolls (in other words, if streaks happen, they're just random).

I'd still like to run some tests myself, but honestly all that is good enough for me. I've seen streaks happen as much as anyone, but it appears to me that it's just random when that does happen. Keep in mind that the human brain is notoriously bad when it comes to seeing patterns when there really aren't any; combine that with everyone's inherent confirmation bias and it's really easy to see streaks in VASSAL but forget about all the times there were no streaks. People also rarely understand the importance of sample sizes; a few dozen rolls over the course of a game, even if they are literally all under a 6, doesn't prove a thing and is quite insignificant. You're using n=30 or so, when to get a significant measure of whether or not something like a d20 RNG is random you need something closer to n=75,000 or so.

I posit that VASSAL dice are fair, and it's basically just in your head if you don't think so. Yes, you can have individual games where the dice are "against you" and you roll incredibly poorly or there are streaks, but that is not even close to a sample even worth discussing. It's also important to keep in mind that this happens with real d20s; are those fair? Of course they are (assuming they're well-made and haven't been tampered with). Why do we think differently of VASSAL dice? Probably because when we roll a few 1s in a row they stay up in the chat, taunting us.

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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 9:53 am 
Big Bad Brad
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Ok.

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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 9:56 am 
Death Star Designers
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The_Celestial_Warrior wrote:
Ok.


This is why no one likes you, Brad....

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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 10:00 am 
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The_Celestial_Warrior wrote:
Ok.

That about sums it up.

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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 10:45 am 
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It's an interesting discussion. Honestly it's the conclusion most rational people would come to anyway if they're not in emmotional throws from a game.

I don't play vassal much, and I guess I have heard some people say the rng sucks. But really when I hear people complain about dice (real life or vassal) its not that they think the dice are flawed or the program is either, it's that the small sample of that game sucked for them. It doesn't matter that it's an irrelevant sample to compare to how dice average out over time.

It's like you implied when talking about "big rolls", WHEN you roll a number is more important. You could roll better than your opponent all game, but at the wrong times. You might roll 3 twenties for initiative while you're playing Revan (meaningless), but your opponent rolls that 18 with mace at just the right time. Maybe neither of you has a tactician and you roll an 18 for init (sweet!) then your opponent rolls a 19 (crap!) negating your GOOD roll.

Gamers just focus on the very narrow scope of those bad for them or good for the opponent rolls happening at the wrong time.


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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 10:51 am 
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TimmerB123 wrote:
I don't play vassal much, and I guess I have heard some people say the rng sucks. But really when I hear people complain about dice (real life or vassal) its not that they think the dice are flawed or the program is either, it's that the small sample of that game sucked for them. It doesn't matter that it's an irrelevant sample to compare to how dice average out over time.


I dunno, there is definitely a lot of complaining and supposing that the VASSAL RNG actually is flawed in some way. Interestingly, in my research this morning I found this all over the place; lots of people use VASSAL to play Warhammer, and there are threads on www.dakkadakka.com (Warhammer forums) about how they think that VASSAL dice are "worse" than real life dice. I think it's a combination of confirmation bias, remembering only the extreme events, and basic innumeracy (specifically in not understanding how statistics or sample sizes work).

It's not logical and you wouldn't think it's true, but people do blame the program or even the actual dice for bad rolls. Once at GenCon during the lunch break of the championships (I believe this was '09), Graham and I talked to a guy who insisted that his die was "bad" and that it rolled an average of a 5 or so. There's no way his die was that bad; he was just focusing on the bad rolls and had a very small sample size (just 3 games with it).

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 Post subject: Re: VASSAL Dice
PostPosted: Thu Jun 21, 2012 11:07 am 
Imperial Dignitaries
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Yep, sometimes the dice just turn against you, and sometimes they turn for you. There's really nothing you can do about it. Sometimes on Vassal after a particularly bad streak I've said, "ok, hold on for a sec, gotta clear the dice :)" and then I've clicked the dice roller about 10 times. It might not make an actual difference, but it sure does make a psychological difference! :D

I think we often highlight certain rolls in our minds, and remember only those dice rolls. Example: on "the big init" you roll a 2, but on your 3 attack rolls prior to it, you had a 13, 17, and 12, but those attacks missed because they were potshots with scrubs that missed anyway. Those attacks rolls didn't register in our minds because they were insignificant, but the init roll sure did register!

I've had games where I "got Vassaled." One time, after a particularly bad "Vassalling," I went back through the game and recorded all of my dice rolls on paper, and calculated the average roll...it turned out to be something like 10.5, which is just what it should be. I had just rolled 20s on insignificant inits and 2s on significant attacks, etc. So if this was the case in a particularly bad Vassalling, then I don't think things are really as bad as we sometimes seem to think. We are getting good dice rolls, but they just aren't coming at the most opportune times.

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 Post subject: Re: VASSAL Dice
PostPosted: Fri Jun 22, 2012 1:13 pm 
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vassal does seem to hit trains of long low or high numbers.

Its been tested before by nickname and co and generally there is no bias or algorithmic trend that causes it. The numbers, with a high enough sample, always average out to the mean so long as you take all the dice scores of the game.

The problem is that a game of minis isn't a terribly high sample so if you get a low run over a round or two it appears appalling probabilistically but in the scheme of things its just a road bump well within expected variation.

I've often accused vassal as being bust, but i've done the same to dice.

Best to not let it get to you, the random nature of minis dice is part of the game. If you bank on the right percentages and probabilities in the long run you'll come out ahead, like in poker.

Its just sometimes that crucial few rolls will let you down.

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 Post subject: Re: VASSAL Dice
PostPosted: Fri Jun 22, 2012 4:18 pm 
Really Cool Alien from a Cantina
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Nuh uh! My anecdotes >>> your stupid numbers. Vassal dice r brusted!!!111!!1

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 Post subject: Re: VASSAL Dice
PostPosted: Fri Jun 22, 2012 10:31 pm 
Moff Disra
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fingersandteeth wrote:
Its just sometimes that crucial few rolls will let you down.

In the early days of SWM, I think there were fewer "crucial rolls" in a game. Currently, I think there are two init's and at most three attacks rolls a game that are "crucial". If all the other rolls are about normal and you win these few, you have won the game.

At one point, I was keeping track of my rolls. It became pointless to compare an attack roll of 15 (needing let's say a 9) to an init roll of 15 (when I lost to a 16). Which was the more important roll? Was the init roll the first init or that critical third turn init?


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 Post subject: Re: VASSAL Dice
PostPosted: Sat Jun 23, 2012 5:25 am 
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greentime wrote:
Nuh uh! My anecdotes >>> your stupid numbers. Vassal dice r brusted!!!111!!1


I count 4 1's in a row there Grahm.
I've had 5 1's in a row in live game and lost 3 Jedi to palps sl and his betrayal when he was the only fig left for my opponent back in the days of ROTS.

My 2 cents (from a guy who doesn't have a computer to play vassal) (if we could only make into an iPhone app like ascension)
I can't believe it is any different from live rolling. I've had streaks of high numbers and streaks of low.
I've had 3 people that I would consider to be in my normal playgroup all tell me that I either roll hot or I roll cold, that there is no inbetween or middle ground with my rolling.

Like I said, I don't play vassal (I wish I could) but that is just my 2 cents. Take it as you will.

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