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Probability distributions etc

 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 9:17 pm 
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Ulrik wrote:
One point I continually have to make for myself is that if you will, on average, win by four, that is not a safe assault. The odds of losing that is pretty high, guessing something around 30%.

carlos wrote:
If on the other hand you're bothering about the 2*5+/3+ difference for a single unit in a game of toy soldiers that is published by the users w/ no commercial implications, then you're bothering too much.


Units usually come in formations. Take 8 of those 2x5+/3+ and you start to see some significant differences.


Especially because probabilities are non-linear.


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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 10:02 pm 
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The great thing about 'doing the math' is that it can completely change one's viewpoint (our intutition is often way off when it comes to stats). The trouble is that it totally disrupts threads (which understandably annoys those who believe math to be meddlesome trickery that sucks all joy out of the game).

I suggest that from now on, we have a "let's take this one outside" convention. If anyone wishes to challenge a statistical assertion, then they state that they wish to "take this one outside". The belligerants may then switch to this thread and attempt to math-hammer the other into submission; meanwhile the original thread can move on. The mathletes can subsequently return to the original thread with their conclusions (if anyone beyond them still cares by that point).

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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 10:20 pm 
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adam77 wrote:
I suggest that from now on, we have a "let's take this one outside" convention. If anyone wishes to challenge a statistical assertion, then they state that they wish to "take this one outside". The belligerants may then switch to this thread and attempt to math-hammer the other into submission; meanwhile the original thread can move on. The mathletes can subsequently return to the original thread with their conclusions (if anyone beyond them still cares by that point).


It's a good suggestion. However, maths should have a place in any game with probabilities, so any conclusions from the maths thread should be respected, even if you're a mathophobe yourself.


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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 10:24 pm 
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Ulrik wrote:
...so any conclusions from the maths thread should be respected, even if you're a mathophobe yourself.


Good luck with that ;D ;D ;D

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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 10:53 pm 
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It´s quite simple really:

3+ is great if you need a certain number of sure hits.

5+ has the same probability, but you can get two hits (you will never do that with 3+, so this option is stronger).

They are not the same, that is clear, but what about simplicity?. Why even think about 2x5+ having the choice of 3+??, Why not keeping 1 die per unit and therefore avoiding having to roll dozens of dice, making everything simpler and faster (I mean simplicity, not lack of tactics)??

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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 10:56 pm 
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Kyrt wrote:
That is because the chance of getting average hits or better is actually only 50/50.


4+
avg hits = 1/2
chance of getting average hits or better = .5

2x4+
avg hits = 1
chance of getting average hits or better = .75

1+
avg hits = 1
chance of getting average hits or better = 1.

typically, chance of getting average hits or better > .5

?


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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 11:02 pm 
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Kyrt wrote:
I will put forward the argument that considering variance can give you a modest advantage as a general and is worth considering for list design.


Knowing and considering the variance of the probability of rolls can and does give a player an advantage as a table top general, I can vouch for that personally .

Having worked on quite a few lists in the last couple of years I'd say it is taken into account very early on in the process of list design, especially when concerning formation sizing, extra attacks, ranged attacks etc. .


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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 11:09 pm 
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In all honesty, I want to understand all this but my brain does not let me - It must be why I'm a crap-ish general :D


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 Post subject: Re: Probability distributions etc
PostPosted: Wed Oct 26, 2011 11:56 pm 
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Before attemptimg more in-depth anaylsis, we should stop abusing the term 'variance'. Variance is a well defined parameter you can calculate for a distribution, it gives some useful information but it doesn't tell you things like range of possible values, skew, inter-quartiles, etc. E.g. you can have two distributions with equal variance and mean, but very different ranges.

When talking more generally about the spread of values I suggest using the term 'variability'*, which itself can be described using, for example, variance, range, inter-quartiles, etc...

*'swingy-ness' is also popular

@Dobbsy, never underestimate the General's gut instinct! Fire beats Ice (sort of) etc... ;D


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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 1:10 am 
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I do all the maths in my head when I play, but the sample sizes are so small in this game that anything can happen. It is particularly laughable when a list is mentioned as being fully playtested and it's had all of 12 or 20 games - and those games are random ones, not specific setups to test each situation a 100 or a 1000 times. Then again, that's the industry (ie GW) standard anyway.
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some of us like really detailed painting, some of us like really detailed thinking.

Nothing in this topic is really detailed thinking and the patronising tone is very off-putting.

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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 1:49 am 
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Ulrik wrote:
One point I continually have to make for myself is that if you will, on average, win by four, that is not a safe assault. The odds of losing that is pretty high, guessing something around 30%.


Not quite, if you are on +4 for combat resolution then the only way to lose the assault is to roll double 1 whilst your opponent rolls a 6 on either of their two dice.
If you do roll a double 1 (which has a 2.777....% chance of occuring) only then does your opponent have a 30.555....% chance of winning by rolling one 6 on either of their two dice.
I believe this works out roughly at around 0.909 % chance of actually losing the assault from being on +4, although it does feel like it happens more than that :-[ .


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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 2:18 am 
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dptdexys wrote:
Ulrik wrote:
One point I continually have to make for myself is that if you will, on average, win by four, that is not a safe assault. The odds of losing that is pretty high, guessing something around 30%.


Not quite, if you are on +4 for combat resolution then the only way to lose the assault is to roll double 1 whilst your opponent rolls a 6 on either of their two dice.
If you do roll a double 1 (which has a 2.777....% chance of occuring) only then does your opponent have a 30.555....% chance of winning by rolling one 6 on either of their two dice.
I believe this works out roughly at around 0.909 % chance of actually losing the assault from being on +4, although it does feel like it happens more than that :-[ .


A fair point... though I'm not sure that Ulrik would disagree with you -- the way I read him, he was trying to set up assaults that would probably result in a +4 differential (a sure thing, as you point out)... as insurance against bad hit rolls and good saving throws. The interesting thing about assaults is that the variation within the combat resolution can lead to fairly sharp swings in the final differential -- vis. a 10-4 assault can work out to 7-4, losing one of the presumed modifiers, you can lose your inspiring character, and you can fail to inflict any casualties -- and suddenly you're rolling at -1.


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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 2:33 am 
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carlos wrote:
Nothing in this topic is really detailed thinking and the patronising tone is very off-putting.


It was more in response to your statement that we were over thinking it or wasting our time.

Stuff like the difference in performance between 2x5+ and 3+ is important.

I don't like sending my troops into something unless I know how much they are likely to kill, and how badly they might fail.
With a formation of 10 units say, I'd actually expect the 2x5+ to be closer to the average then the 3+ (the opposite conclusion of Kyrt). Now I'm going to have to go away and check the probability distribution for them both. Binomials ahoy!

EDIT: and done.
bugger. kyrt was right.

It is interesting to note that the curves aren't symmetrical, but they are probably close enough for head maths during a game.


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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 9:27 am 
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Carrington wrote:
A fair point... though I'm not sure that Ulrik would disagree with you -- the way I read him, he was trying to set up assaults that would probably result in a +4 differential


Yup. I was thinking situations where you "on average" should come out with +4 (ie your estimate before rolling attacks). If you need to be sure I think you need something more like an expected +8.

Like madd0ctor I had always assumed that more dice gave a more reliable result (because xd6 produces a tighter bell curve with higher x), so I was surprised to discover that it isn't so. For list the design I think that's a good thing actually, because a single 3+ "feels" like an elite, precision unit while 2x5+ "feels" like something more wild and chaotic - and it matches up with the maths.

Now we need to campaign for Khorne Berzerkers to be changed CC2+to CC6+, EA+4 :)


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 Post subject: Re: Probability distributions etc
PostPosted: Thu Oct 27, 2011 9:56 am 
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dptdexys wrote:
Ulrik wrote:
One point I continually have to make for myself is that if you will, on average, win by four, that is not a safe assault. The odds of losing that is pretty high, guessing something around 30%.


Not quite, if you are on +4 for combat resolution then the only way to lose the assault is to roll double 1 whilst your opponent rolls a 6 on either of their two dice.
If you do roll a double 1 (which has a 2.777....% chance of occuring) only then does your opponent have a 30.555....% chance of winning by rolling one 6 on either of their two dice.
I believe this works out roughly at around 0.909 % chance of actually losing the assault from being on +4, although it does feel like it happens more than that :-[ .

That's true, but the point was about the chance of achieving your average number of hits in the first place not being particularly high.

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