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Question of the Day - 09 August 2024

Q:

On a video poker machine, does playing more lines increase the variance of the game? Does playing a higher denomination increase the variance of the game? 

A:

[Editor's Note: We started discussing this question and got bogged down almost immediately. Instead of begging off it, we offered it to a good friend of LVA, whom regular readers have seen on occasion in comments and expertise in the answers. Stewart Ethier is one of the world's top gambling mathematicians and a gambling historian/scholar par excellence. His answer is direct evidence that seemingly simple questions, like this one, can actually be quite complex.]

That's actually quite an interesting question, which I've thought about before. Here's my answer, explained as simply as I can.

First, a few remarks on terminology. Everyone knows the term expected (or mean) return. It is the long-term average return. For example, at 9/6 Jacks or Better with a one-unit (max-coin) bet, it's a weighted average of the 10 possible payouts (800, 50, 25, 9, 6, 4, 3, 2, 1, 0), weighted by the probabilities with which they occur.

800 (0.000024758268) + 50 (0.000109309090) + ... + 0 (0.545434669233) = 0.995439,

often written as 99.5439%. The variance is the expected squared deviation from the mean. In our example, it is

(800 - 0.995439)^2 (0.000024758268) + (50 - 0.995439)^2 (0.000109309090) + ... + (0 - 0.995439)^2 (0.545434669233) = 19.5147.

The variance determines the game's volatility by virtue of a result known as the central limit theorem. Alternatively, one can consider the standard deviation, which is the square root of the variance, the advantage being that it is measured in the same units as the payouts themselves (e.g., dollars instead of squared dollars). In our example, the standard deviation is 4.41754 units, while the variance is 19.5147 squared units.

Now, let's consider the easier second question first and let's work with standard deviation (the square root of the variance) instead.  

If the random variable X is the payout from a one-unit bet, then bX is the payout from a b-unit bet, and SD(bX) = bSD(X). So the payout from a bet of size b has standard deviation proportional to b.  

Example: In 9/6 Jacks or Better, the standard deviation of the payout from a one-unit (max-coin) bet is 4.41754. So for a $5 bet, the standard deviation is $22.09. For a $25 bet, it is $110.44.

Ultimately, the answer to the question depends on what is meant by the standard deviation of the game. If it is the standard deviation of the actual payout (e.g., $22.09), then the answer is yes: Playing a higher denomination does increase the variance of the game. If it is the standard deviation of the "payout per unit bet" (e.g., 4.41754), then the answer is no. For what it's worth, I prefer the latter interpretation.

For the first question, I'm assuming that the questioner meant a multi-play video poker machine (instead of multi-line). This is also an interesting question that has been discussed in at least two sources. Its answer again depends on interpretation. 

Hannum and Cabot, in Practical Casino Math (2005, p. 162), wrote, "Without delving further into the mathematics, suffice it to say that for multi-play video poker, there is no change in the expected value (house edge), but the variance (volatility) increases." Ethier (that's me), in The Doctrine of Chances (2010, p. 568), wrote, "In n-play video poker, the variance of the 'payout per unit bet' is decreasing in n."

This apparent contradiction is the result of different interpretations. Let S_n be the sum of the payouts from the n plays, assuming one unit bet on each play. Hannum and Cabot were referring to Var(S_n)/n, which is increasing in n, while Ethier was referring to Var(S_n/n), which is decreasing in n. The justification for the former is that this would be the appropriate normalization if betting on n independent single-play machines. The justification for the latter is that, when comparing single-play and n-play machines, total amount bet should be the same, namely one unit. Not surprisingly, I prefer the second approach.

Notice that we are not providing a numerical example here. What is Var(S_n/n) with n = 10 for 9/6 Jacks or Better? Nobody knows! It has not been computed, to the best of our knowledge. We leave it as a challenging exercise for the interested reader.

 

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Comments

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  • Kevin Lewis Aug-09-2024
    This got obscure kinda fast
    It's real simple. A given game has a given variance, which should properly be expressed in betting units. Thus, the denomination played doesn't matter, as long as the paytable is the same.
    
    A multi-line game has less variance than the same game with the same paytable in a single-line version would have. If someone says "multi-play" game, that's what they're referring to--a multi-line game.
    
    If a player wishes to minimize variance, he can a) play inherently less volatile games, b) play multi-line games (for the same total bet per hand), or both.

  • Patrick McCann Aug-09-2024
    Krusty the Clown said it best
    What the hell was that? 

  • Donald P Jaspan Aug-09-2024
    QOD 8-9-24
    Huh…hows that again?

  • Vegas Fan Aug-09-2024
    As my old boss would say... 
    After giving a lengthy explanation to a question asked of him, would say"now, are you sorry you asked?" 

  • AL Aug-09-2024
    Some laymen's talk
    Here's a tangible example of why playing multiple hands/lines has less variance/volatility than playing a single line. If you get dealt 4 of a flush, your chances of getting a 5th card of the same suit are 9/47, or close to 1 out of 5. So, on average, you will fill the flush about 1/5 of the time, but you can easily go 10 times without filling it, and might go 15 or 20. But on a 5-play game, when you get dealt 4 of a flush, the chances are high that you will fill a flush on 1 or more of the hands, so you will have a more even-keel time, and very likely won't experience ZIP, ZIP, ZIP, etc., on a succession of deals that give you 4 of a flush. The variance is lower, and the volatility is lower. I have no idea what Hannum and Cabot are referring to when they say that these will be higher. NOTE: I do not think denomination (size of bet) should be considered when discussing variance/volatility. These terms are about proportionality, i.e., results seen in relation to your size of bet.

  • Trainwreck Aug-09-2024
    Higher Denomination 
    The denomination of the wager shouldn't affect the variance (as Kevin opines) but is it possible the questioner wondered if the results were 𝘸𝘦𝘪𝘨𝘩𝘵𝘦𝘥 differently at higher denominations (assuming this was even possible)?

  • jay Aug-09-2024
    It depends
    It really depends on your interpretation of variance.
    If you play a $25c game win or lose you have a $25c variance 
    If you play a $1.00 game you could consider your variance to be 4x larger.
    It follows the adage bet more/win more (or lose more).
    However from a %% win or lose both are the same.
    
    
    In a multi hand game if they each are dealt from a fully randomized deck then the only thing that changes is speed of play. If they are all dealt from the single deck of cards then we would be back to the blackboard. 

  • O2bnVegas Aug-09-2024
    April 1st?
    I stopped to think of today's date.  LOL.
    
    How great to have the brain for math as Mr. Ethier does.
    
    Candy
    

  • Marcus Leath Aug-09-2024
    That answer is why I failed calculus
    I play the best possible available video poker pay schedules.  I do not worry about any of the mind-boggling math issues.  I use Bob Dancer's pocket cards all the time when I get a difficult hand dealt to me.  Of course one does not need a guide when one is dealt 4 to a Royal or some such hand.  The complex answer to the questions posed just shows why the average player does not need to "understand" higher math.  When I was a freshman in college, the first class I attended in my calculus course was taught by a guy who began speaking in the same confusing way this answer was given - no basic explanations, just jargon.

  • O2bnVegas Aug-09-2024
    math, smath
    A simple example why I don't stress over it.
    
    Say I'm playing 3 Play VP JOB or most any game. I'm dealt Q-Q-Q-10-4. I (and most) would hold the 3 Qs, discard the 10 and 4, hope the fourth Q fills in on one or more of the three hands.  Is there any other way to look at it?  But one never knows, and will never know, what might be/would have been lurking under those Qs on the other two hands.  Maybe something that would make up a better hand on the draw, such as the 'other' Q suited with the rest of a Royal Flush.  Not likely, but good thing we'll never know.  JMHO.
    
    Candy

  • sunny78 Aug-09-2024
    point of lunacy
    Isn't there a limit in everything where the analytical component goes 301x too far over the rainbow to the land of, what's the point? I think this is an illustration of that point. Want to make money? Increase your odds of it? Don't gamble. Get a job, invest.  

  • Lucky Aug-10-2024
    Lunacy
    Sunny has it right.  Want to win more often, don't bet on something that you do not already have the answer to.  How about this question.  Where do you have a better chance of winning or coming out ahead?  VP or the stock market.  Talk about variance in the last 2 weeks!
    

  • Stewart Ethier Aug-19-2024
    Update
    I can clear up a loose end left by the original answer.  In 9/6 JoB with a max-coin bet and with n plays, the variance is given by the formula
    
    Var = (1/n)19.514676427086+(1-1/n)1.966388673536.
    
    For 1-play, 3-play, 10-play, and 100-play, respectively, we get 19.5147, 7.81582, 3.72122, and 2.14187 for the variances.  Take square roots to get the standard deviations.
    
    Apologies for making the original answer more complicated than necessary.
    

  • Stewart Ethier Sep-23-2024
    Update 2
    Here is a more complete answer to the multi-play video poker question:  https://arxiv.org/abs/2409.03607.  Go there and click on PDF.
    
    In particular, the original answer was misleading to suggest that the Hannum-Cabot claim was simply an alternative interpretation; in fact, it was wrong.