Steve Jacobs wrote:
> ER and EV are different forms of the same basic concept. I don't
> see how one can be "awkward" while the other is clear.
Perhaps I'm mistaken then. However, my take is that EV is an absolute
value.
If that were the case, we would never talk about "negative EV," but that
phrase pops up all the time. A favorable game has an ER greater than 100%
and a positive EV. An unfavorable game has an ER less than 100% and
and negative EV.
For example, if a possible outcome of an event is a reward of
100 credits and there's a 60% likelihood of that outcome (and 40% of a
0 credit outcome) the EV is 60.
Strictly speaking, this represents an ER of 6,000%. This is a "no lose"
scenario, and those are rare in gambling situations. No-lose scenarios
always have non-negative EV.
In Ed's "Save the Queen" example, in
holding 4 to the Royal the EV is a 49% chance of saving your ass.
This should probably be ER instead of EV. Of those players exposed
to the game, 49% are returned alive. That is an EV of -51%.
ER is, as the administrator defines it, EV/coin-in. If there is no
coin-in, as in this example or a tournament (where EV is based upon
the tournament prizes), I find application of the term ER "awkward".
For a tournament, the "coin-in" is the entry fee. For the life/death
situation, the "coin-in" is a live body. But, I think the definitions in
the FAQ are misleading at best, and should be updated.
l'll use E[expr] to represent the expected value of some mathematical
expression that is represented as "expr". When the initial bet is treated
as a single unit, it is represented by a value of 1. ER (expected return)
is then:
ER = E[1+X*p(X)] where the "1" is the initial bet, X is a particular outcome
like +10 bets or -1 bet, and p(X) is the probability of that outcome. Summing
over permitted values of X gives the exptected value of the expression.
ER can be expressed as a pure number like 1.0123, meaning that the
game returns an average of 1.0123 units for every unit played, or it
can be expressed as a percentage of 101.23%. Either way expresses
the total amount returned to the player.
EV simply removes the original bet from the equation, and expresses
the CHANGE in bankroll as a result of the wager. So, we have:
EV = E[X*p(X)]. This can be positive or negative, depending on
whether the average outcome represents a gain or a loss for the
player. EV can also be expressed either as a pure number or as
a percentage. For the case described above with ER, the outcome
here has an EV of +0.0123 units or +1.23%. It might be more
mathematically precies to call this EG for "expected gain," but it
doesn't matter much since terms like EV/EG/ER and not used
consistently, so you have to read carefully to figure out the
author's meaning from the context.
So, we have at least 4 ways to decribe the same concept. We can talk
in terms of EV or ER, and we can talk in terms of units or percentages,
but they all boil down to the same thing after the dust settles.
> Mathematically, this is changing to a different random variable for
> which we maximize expected value. The max-EV strategies for VP
> are based on maximizing "mean bankroll after one play". The random
> variable in this case is "player is alive (value =1 if true, 0 if
> false)".
I'm not sure what you mean by "changing" since there isn't any other
economic variable to maximize in this instance.
Not true. The player can still choose to maximize the EV of the bet
itself. That wouldn't be my choice, but maybe the player is suicidal 
Using death as an outcome makes the situation too extreme, so let's
reduce the penalty for losing. Also, let's assume that you be faced
with such a situation one week from today, so that you will have time
to prepare an appropriate strategy for any situation that might turn up
on the VP machine. Consider the following possibilities:
Result of Losing:
1) Certain Death
2) Mostly Dead (a la "The Princess Bride")
3) Loss of a pinky finger
4) Public humiliation (perhaps dropped off naked in Central Park)
5) Forced to endure a bad hair cut (perhaps a shaved head)
6) Forced to listen to a one hour lecture on "The Evils of Gambling"
7) Laughed at and verbally abused by your captors.
8) No extra penalty whatsoever.
For case 1), rational people would likely to be interested in learning
the playing strategy which absolutely minimizes the probability of
losing.
What about case 5)? How much monetary EV are you willing to
sacrifice do keep your hair intact? For those who already sport
a cue-ball, this reverts to case 8, but some this would be almost
like case 1). So, faced with this situation, the "optimal" strategy
will be different for different players. That doesn't make one player's
choice "better" than anothers, only different. What is best for you
and your hair implies nothing about what is best for me and my hair.
I put forth that this is true in general, and not just for this kind of
special situation. The CHOICE to maximize EV is not inherently
the "best" choice for every person, and alternate strategies exist
that are every bit as mathematically justifiable as maximizing EV.
The problem with max-EV is that is gives no weight to considerations
of overall risk, is only considers reward.
For case 8), the "experts" would mostly say "play max-EV strategy".
Case 8 is the one where I claim there are other "mathematically
correct" alternatives that should be considered, but which the
"classical" VP experts never mention. Factors of risk, time constraints,
or other considerations are left out of the max-EV equation. Including
these factors leads to different strategies that are just as valid as
max-EV. Those who believe that max-EV is the only "correct"
approach are mistaken.
> Personally, I don't think Ed is particularly confused. He has
> discerned a subtle point -- optimal strategies don't exist in a
> vacuum, they depend on your choice of which random variable is used
> as the basis for solving the optimization problem. The "usual"
> definition of EV is based on one specific random variable, but there
> are often (if not always) alternatives which are worth considering.
Perhaps, however Ed's post suggested that someone might approach the
"Save the Queen" example by desiring to optimize the credits on the
machine meter, which in themselves have no economic value. I don't
think Jean, or anyone else for that matter, suggested that's what
"perfect strategy" is about. It's about optimizing the economic value
at hand, at those credits have no economic value.
You're assuming the player won't receive those credits if they survive.
If the conditions are "you lose, you die, but if you win, you get the
payoff" then they credits have economic value. If the payoff is big
enough and the probability of losing small enough, the I'd submit
there is a point where it is worth risking your life in order to win
a sufficient reward. Example: you get a 99.99999% chance of winning
$10 million, but if you lose you die. Give a legitimate offer from people
who I absolutely trusted, I'd accept such a proposition, because it
amounts to a virtual certain win. My risk of keeling over from a
heart attack in my sleep tonight are much higher than my risk of
death from such an unlikely event.
But Steve, I hope that I haven't suggested that there aren't alternate
variables in a given case that might be chosen for optimization.
Take a variation on "Save the Queen". Let's assume that what's at
risk are the lives of 10 members of the royal family (all of whom are
equally valued). The choices are a default that 6 are killed, or they
may opt to spin a wheel with 11 equally weighted outcomes (0 to 10
deaths) - EV number of deaths = 5. Spinning the wheel is "optimal" in
reducing the expected number of deaths, however, the family may choose
to fix the deaths at 6 rather than risk that a much greater portion of
the family may be wiped out.
Actually, this is a risk preference problem that's akin to why someone
might opt for a lower risk (variance), lower return VP game over one
with higher values of each.
Agreed.
But once one has selected a game to play, there are extraordinarily
few circumstances under which EV/ER aren't the variables to maximize.
Again, I don't deny that some don't exist. But in a vp group such as
this, while it's important to acknowledge that such circumstances
exist, it's critical to suggest that they're few and far between for
the typical player and that EV/ER is the thing to stress.
I used to believe this, but I no longer do. There has been too much
emphasis on EV for too long. Those who take gambling seriuosly hear
so much thumping on the max-EV drum, that the more subtle parts of
the melody are competely lost (if they are "played" at all by the authors).
Readers are left with the mistaken impression that anyone who doesn't
maximize EV is simply wrong and that max-EV is the only "intelligent"
way to play. I constantly see posting on this forum that echo that very
sentiment.
My message: Free Your Mind. If you believe that max-EV is the one
true way, and no others can possibly exist, then you have either
misunderstood or been led astray by "experts" who don't fully comprehend
all of the mathematics that comes into play when finding optimal strategies.
(I don't mean that to be directed at Harry, who has one of the freest minds
around).
Otherwise, you get the suggestion that it may be reasonable to
sacrifice considerable EV/ER to assure a greater likelihood of a RF.
Let me turn that around. The problem with the prevailing max-EV
mentality is that it precludes almost any consideration of the possibility
that sacrificing EV/ER may be correct. "Just maximize EV period" is
the wrong answer, but it is pretty much what the experts tell people
to do.
The problem with the status quo is that we have rampant opinions in
the opposite extreme -- too many people don't understand that there
are very meaningful considerations other than max-EV. People have
become max-EV zombies who have been so totally ingrained with
the max-EV message that they no longer give ANY consideration to
other options. To some extent, this can be traced back to experts
who themselves believe too much in max-EV, and who have forgotten
(or perhaps never knew) that EV isn't everything.
That's simply unsound strategy if you're going to play the game
rationally. You might very well use comparable reasoning to suggest a
player hold any and all red cards because they get very excited when
the final hand is entirely red.
As you know, I'm not advocating irrational play, and the things I'm talking
about can all be reduced to mathematics. Also, I'm not claiming that
it isn't rational to maximize EV, I'm only trying to point out that max-EV
isn't the ONLY rational way to play. Also, in this context I would
define "rational" as "mathematically justifiable in order to meet a
stated objective."
There simply are other games they should play if that's how they get
their kicks, not one in which they have money at risk.
Well, it is their money to risk, and if they TRULY enjoy getting a final
hand that is all red, and that brings them sufficient happiness in
exchange for the monetary cost, then I won't claim that they got poor
value for their entertainment dollar. However, that isn't something that
can be easily reduced to mathematical terms, so it isn't really the kind
of thing that I'm talking about.
···
On Saturday 04 October 2003 08:37 am, Harry Porter wrote: