Introduction
Game theory is an essential framework for analyzing strategic interactions among individuals or entities where the outcomes depend not only on one's decisions but also on the choices of others. Today, I'm excited to delve into the foundational aspects of game theory as we explore various examples, particularly in economics and competitive scenarios.
What is Game Theory?
Game theory is essentially the study of how participants make decisions in competitive and cooperative settings. It finds applications in economics, politics, psychology, and more. The crux of game theory lies in strategic dependence—the idea that your choices are influenced by others' decisions.
Economical Examples
Consider the rivalry between two firms in the tech industry, like Apple and Google. Here, both companies strategize on pricing, product development, and marketing based on their competitor’s expected moves. Another example might involve cooperation, such as collaborative efforts among deans and vice presidents working towards common goals.
Game Theory in Action: The Sponge Duel
To illustrate the principles of game theory effectively, let's consider a light-hearted sponge duel involving two participants. The rules are simple but elucidate some complex dynamics within game theory.
Setting Up the Duel
Two deans from Yale, Robert Post and James Bundy, are selected as players. Each has a sponge and must decide whether to throw it or step closer to their opponent. The outcome hinges on their choices:
- Throw the sponge at the opponent.
- Step forward.
Analyzing the Decisions
At any given turn, a player can evaluate their opponent's potential moves. The aspect of strategy becomes crucial here. If one player decides not to throw, the other might perceive this as a signal to take a step forward, leading to further strategic positioning.
Key Observations
- If Player One Throws:
- Probability of hitting the target decreases with distance.
- If the player misses, they become vulnerable.
- If Player Two Steps Forward:
- They might gain a better shot if they decide to throw afterward.
This scenario leads us into concepts like backward induction, where we assess the future implications of current decisions.
Practical Applications of Game Theory
Business Strategy
In business, timing is crucial. For instance, if two companies are launching technological innovations, deciding when to enter the market can drastically affect their competitive standing:
- Launch too early? Risk being untrusted by consumers due to unrefined products.
- Launch too late? Risk losing market position to competitors that have established themselves.
Sports and Competition
In sports, athletes often use strategic decision-making akin to game theory. Decisions made during a match can hinge on predicting the opponent's actions, akin to evaluating when to throw in our sponge duel.
Dominance and Backward Induction in Game Theory
Understanding Dominance
The concept of dominance in strategies suggests that certain actions will always yield better outcomes regardless of the opponent's choices, enhancing strategic clarity.
Backward Induction Explained
Backward induction is a method of reasoning that allows players to anticipate others’ future moves and adjust their strategies accordingly:
- Start from the end of the game and reason backward to determine the optimal strategy.
- This technique is essential for making informed choices in competitive environments.
Practical Takeaways
- Avoid Early Moves: In our sponge duel analogy, players should not throw their sponges until crucial distances are reached, maintaining leverage.
- Rational Reflections: Assess the rationality of your opponents' responses to your actions, further refining decision-making.
Conclusion
In conclusion, game theory provides a robust framework for understanding strategic interactions in various settings, from business to everyday decision-making. By recognizing the significance of timing, dominance, and backward induction, individuals can enhance their strategic prowess, be it in business contracts or playful sponge duels. Embracing these principles enables better outcomes in competitive and cooperative environments, reflecting the nuanced interplay of human decisions and interactions.
Learning the intricacies of game theory not only improves individual strategic thinking but also fosters a deeper comprehension of collective behavior in economics and beyond.
uh I'm Ben poac I'm proost of Yale but in real life I teach economics I teach Game Theory um so I'm actually going to
get rid of the jacket if you don't mind um and go back to my life as a professor for a for an hour um I've actually never
given a talk in anything like this before uh kind of amazing Church a church with a small group of people in
me we're going to talk about Game Theory um game theory is the analysis or a way of analyzing strategic situations so
what are strategic situations strategic situations are any setting where the things that you care about the outcomes
you care about depend not just on your own actions but on the actions of someone else all right so let's think of
some examples but we won't stay along with examples uh in economics the an obvious example would be two firms who
are competing in the same Marketplace so think of Apple and Google Apple and Samsung right they're both competing in
the market to make uh telephones to make these things whoops just knocked off the mic make these things and they have
various strategies available to to each other pricing quantity innovation suing each other bribing jewes whatever else
they do all right so that's a game involving players where they're competing but it isn't only competition
that we can model we can also model settings of cooperation so think about teams working on in the same firm or uh
looking around the room groups of Deans and vice presidents of Yale who are working together uh to try and get
things done so so game theory is also the way you analyze how to herd cats all right roughly speaking all right so when
we teach game through at Yale uh what we do uh is we try to play games in class and we analyze them as a way of seeing
uh you know teaching the technique but also learning about the game that's a technique of teaching that's now spread
uh pretty much worldwide uh and it's what we're going to do today so today I'm going to play a game we're going to
analyze that game we're going to play the game we're going to analyze that game and we hope I hope we're going to
learn something as we're going along okay so that's what we're going to do um uh if some of you have seen this game
being played online if you've seen my online courses uh and uh if you haven't uh a a plug in for looking at the L
online courses not just mine but everyone else's as well so I need two volunteers for this and uh rather than
embarrass people I'm just going to pick people out so I'm going to pick two deans who happened to be here who didn't
know this was going to happen uh I'm going to pick Robert post who's here and I'm going to pick James Bundy who's
there and I'm going to drag them out the front uh so so uh and the reason one reason for picking on these two deans is
this is a day to celebrate Yale and uh Robert post is the dean of the law school uh which is quite simply the best
law school in the world and he is quite simply the best Dean of the best law school in the world and James Bundy is
the Dee of the drama school which is the best drama school in the world and he is quite simply the best Dean of the best
drama school in the world so why don't we have a little plug for our our wonderful schools while we're here okay
so the audience provides the volunteers I'm going to provide the props which in this on this occasion is uh two wet
sponges all right we're going to have a sponge fight all right so these are the sponges and I'm going to wet them and
this being Yale I will use nothing but the best I'm going to use Yale University spring water did you know
that Yale University had a spring I don't and we're going to we're going to wet these and uh the people who who are
custodians to this building are look away for a second cuz I'm going to dribble water on the floor
and Bruce is back there and he's thinking the facilities bill is going to us so don't look for a second
Bruce right and I'm going to squeeze these out and try and make sure they're roughly
blue sponge and a green sponge I'm going to give the blue sponge to James Bandy and I'm going to give the green Spong or
post and a minute I'm going to position them at either well I'm going to do it now I'm going to put Robert here
way all right here we go so we're GNA have a sponge fight or if you like a duel and the rules of the game are this
we're going to have alternating moves all right and when it's your turn to move you are going to have to make a
choice and the choice is going to be whether to throw your sponge at your opponent or whether to take a step
forward all right if you throw the sponge and hit your opponent you win if your opponent throws the uh in case his
sponge and hits you you lose right simple simple rules we'll need a few specifications one important
specification uh is uh well the most important spe is this each player only has one sponge and once they've thrown
their sponge if they miss the game continues all right so we could work out the strategy this in great detail but
let's not let's just realize what's going to happen so if you throw your sponge and you miss since you have to
keep on stepping forward uh eventually uh the other player is going to be right on top of you and it's going to
basically plon his sponge on your head right so if you throw a sponge and and Miss you're GNA lose all right but we
will play that through and see what happens two other rules minor rules each step has to be about a yard right to
keep things fair and this is a rule that I don't know will work in America but let's see uh gentlemen never duck okay
all right all right okay all right so we'll see that okay so everyone understand the rules all right so we'll
make James player one and robot player two I'm exploiting you rather I apologize but Dean's are meant to be
exploited by provos get fit hit in the role so uh James you want to throw your sponge or or a step take a step take a
step okay so so a step and now it's Robert's turn and he's also going to step and now it's James turn he's also
going to step all right now it's Robert's turn step at this point let just pause a second and let's ask people
what they think people should do so it's James's turn you can all see the situation one of the things we think
about in game theory is how to put yourself in the shoes of other people so imagine you're in james' shoes right now
would you throw or would you step step everyone step okay they're all saying they don't trust your arm I don't
know I don't know how you are at baseball as a all right let's have the same question
now for Robert who who thinks he should throw who thinks he should step step they don't really trust their
the arms of the Deans okay all right all right and now yes yes are they allow Doge no dodging no dodging not allowed
not all again gentlemen never do things like that this is a strictly gentlemanly game all right so uh James's turn who
who thinks th it's James's turn who think who thinks throw who who thinks uh you should throw you think throw shano
step well it's up to you don't know know we don't know that we don't know that we don't know and
it's a pretty it's a pretty light sponge we we'll we'll get there we'll get there hold that thought but we will
it's interesting the people at the front are saying throw back got be a coincidence but but but uh you know
David Swinson is saying anywhere on the body anywhere on the body D David is saying throw it he
is the best judge of uncertainty in the in the room so is he on aerodynamic oh not about his
use you in a second um all right so I'm going to victimize our our volunteers a little bit more later um let's talk
about this game a little bit and see we can learn something from it and we were already begin to draw out some lessons
there and we we'll draw out more as we go along so first why is this game interesting so one reason this game is
interesting is uh it corresponds to a duel a duel with with uh uh with muskets I guess bit more serious than sponges
and uh uh for the people in in the room who are Russian literature Specialists you'll know that there are plenty of
duels in 19th century Russian literature a little bit in French literature uh probably the most famous I'm guessing
are the one in War and Peace all right uh and the one one in anen the Pushkin one um or chaikovsky if you prefer that
version uh there are many many others uh in the uh war in peace version uh there are other examples better
examples oh yes up yeah better better more up okay higher higher better it's a big room is that better good okay so in
the uh toy in the war and PE peace version I think we are led to believe believe that the hero Pierre throw not
throw his on shoots his musket too early and he kind of gets lucky and kind of wings dollar off and and uh uh I know
that's a spoiler alert I just but that actually happens about page that's about page 300 in the novel which means it's
in the first half of the book right so there's plenty more after that uh in the uh Pushkin version anden uh anden kills
lsky it's really the critical event of the of the poem um and I think the main lesson we should get from this for
dueling is don't duel right rather than how a duel just don't duel but if you did find yourself in a time machine in
19th century Russia this might help but there's more to this idea than just duels there are games elsewhere where
the critical decision is when to do something there are games when what matters is what you would do and there
are games where what is matter what matters is when you would do it so in this game there's no question about what
you're going to do you're going to throw the sponge but the critical question is when you would do it let me give an
example how many of you have watched the tour France on TV a fair number of you actually surprisingly few but in the
tourto France is a bike race right uh in the T of France in each stage of the Tor Frost one of the critical decisions that
each Rider has to make is they have to decide when to try to break away from the palatin from the pack right and if
you break away too early uh in these long stages uh for sure you're going to be reeled in because over very long
distances the the paleton will go faster than you can go and if you break away too late then either someone else will
break away or just one of the sprinters will win right so the key decision then is is is when to go not when to throw
the spish but when should I break away there's even a movie American movie called breaking away all right so this
is one of the main uh games within a game in bike racing it isn't the main game within the game in bike racing the
main game within the game in bike racing is trying to figure out where to hide your steroids but this is
this all right but this is important uh let me give you an e economic example uh in in or business example in business
you can imagine two firms who are both developing a new technology and that technology could be a new way to uh uh
uh book uh uh air tickets online for example a better way of doing that than the existing one so both companies are
busy doing R&D and trying to perfect this new software or Hardware whatever happens to be and they have to decide
when to launch uh their software and the problem here is if you launch too early when the thing hasn't been perfected yet
it might not work correctly and you're not going to get a second chance right basically if it doesn't work no one's
going to trust you and if you launch too late in this particular Market the market I mean you can think other
examples but this particular market then the other guy will have launched already the other firm will have launched
already uh his or her firm will have established a foothold and probably is going to going to end up becoming the
standard and and being the whole market so this is an example of a market where probably at the end of the day there's
only going to be one player so getting the critical foothold matters but if you go too early you launch too early you're
going to not be trusted by customers if you launch too late someone else will have established them established the
standard so that's about launching a product not launching a sponge but basically the math of it is the same all
right so we're going to analyze this game um we're going to use um these to analyze the game uh and I'm going to do
a little bit of work on the board but I I I want everyone to realize that when I say we I mean we so I'm going to help
along but you're going to solve this with me okay so this is not going to be me lecturing that's what we do it yeah
we get people to participate we just did so we're going to try and learn this together so just to get set things up
before we do that let me just establish a tiny bit of notation uh and draw a picture all right
so just a very simple bit of notation I'm writing kind of small I'm hoping it's going to be visible uh let uh P1 of
D this is the only notation I'm going to use this is the only kind of mathy thing let P1 of D
hits at distance D all right so I'm going to use p1d to say having to write it every time
p1d is the probability that player one who I guess was who was player one was was James hits were he to shoot sponge
at distance D and similarly let P2 of D be the same thing for player all right so I'm going to draw what I think these
probabilities look like I'm going to use a picture all right we're going to use this picture for a while all right so
the notation is not as important as the picture how low can I go before I going to lose the back of of the r oh higher
higher okay is that okay Charles no higher still way high okay in that case I'm going to delete the Top Line and I'm
going to everyone know what p1d is now all right I'm also going to push this back perhaps so you have little bit of
and do it right at the top here that okay is that okay Charles yeah okay good all right so on this axis I'm going to
put D which is distance and on this axis I'm going to put probabilities and I'm going to make some assumptions about the
way in which these probabilities of hitting depend on distance and at least two of these assumptions I think are
inoffensive and the third one is offensive all right so uh the first thing I'm going to assume is that if you
were at distance zero and you shot at distance zero what would what would be the probability that you hit if you
shoot at distance zero one okay so one so that's an assumption but it seems a reasonable assumption so I'm going to
assume that these probabilities start at one if we were at distance zero remember I'm drawing this as a as distance but of
course the game is really going in this this direction right so we're starting far away and getting closer but I'm
going to draw it with distance in the standard way going left to right all right so the second assumption I'm going
to make is that as you get further away the probability of your hitting goes down right so the further away you are
the less likly you are to hit if you if you shoot at that distance so I don't know it could look like it could look
like this say right it doesn't have to be exactly like this I'm just going to assume it slopes downwards all right now
I'm not going to assume that both players are the same here all right so it could be the case that the other
going to say today it wouldn't matter if these things crossed right but all I care about is that they're both downward
sloping so in this case perhaps this one is P1 of D it's player one's probability of hitting and this is player two of D
all right the way I've drawn it who who is the better shot player one or player two player two everyone okay that player
two is the better shot because at any distance we happen to talk about were they to shoot at that distance player
two has a higher probability of hitting they were okay with that so player two is the better shotting now again I don't
need that assumption uh I just need them to be down and sloping it could be that player one is better at shooting at
close distances and player two is better at shooting at long distances that's fine but we'll use this one today
doesn't it w m all right so so far I haven't assumed anything particularly difficult I think here's the difficult
thing I'm now going to make an assumption that's not real uh but I'm going to make this assumption so we can
analyze it today in what is most of your first ever gain three lecture okay so I'm I'm going to make an assumption
that's not true but will help us analyze it it's hard enough even with this assumption all right sometimes it's
useful to make a simplifying assumption I'm going to assume that each player not only knows their own probability of
hitting but they also know the other person's proberbly fitting so I'm going to assume actually I'm assum even more
than that I'm going to assume that these are commonly known so I'm going to assume that player one knows their own
ability they know the other person's ability and they know that the other person knows their ability and so on and
so forth right so I'm going to assume that's all know all right so that's a big assumption but it's it's enough for
today to solve all right I'm going to assume that these are known all right now imagine it
player let's ask ourselves a question who should shoot first the known better shot or the known less good
shot who should shoot first the known better shot or the known plk shot well um um who we are playing the game who
should meaning uh normal you put them in their shoes if you put have in their shoes uh when you're in that person's
shoes from that person's point of view who do you think should shoot shoes first who thinks the better shot should
first raise your hand who thinks the less good shot should shoot first who is hedging their
bets all right so uh let me try and talk it through so the people I'm guessing people who thinking the better shot
should shoot first they're thinking something like this they say well the better shot has a better shot of hitting
the other person at this distance so uh you compare two people at equal distance the person who's more to hit as the
better shot so the better shot should shoot first don't know exactly where they should shoot but they the point at
which they should shoot is earlier since the better shot all right and then the people on the other side I'm guessing
tell me are thinking something like this they're saying well the other gu is a better shot than me so I better shoot
first to preempt him from shooting me is that right and we could take this further then the the better shot could
think hang on a second I know this is all known right so I know the other guy knows that I'm the better shot and
therefore thinks I'm going to shoot first and therefore he's going to shoot first to preempt me shooting him so
maybe I should move even earlier to preempt him from trying to preempt me all right and and we could go on with
this discussion for a while and I think once we've opened up this particular Pandora's Box you can see it's not going
to be that easy right it's not obvious who should shoot first at first it seems obvious got to be the B shot but it's
not obvious at all all right so here's what we're going to do we are going to figure and I'm going to emphasize that
word we again we are going to figure out who should shoot and we are going to solve this exactly we're going to figure
out exactly when they should shoot all right so we're going to figure that out all right for for the physicist and
mathematicians in the room and I can see some you know the answer already but pretend you don't all right all right so
all right on the way I'm going to point out two ideas I hope I remember to do this that are more General than thus
this game all right so we're going to work through this game but since I want to use this as an illustration for ideas
you might use elsewhere in Life or when you're playing games or wherever I'm going to try and draw out two larger
forget okay oh I brought Pushkin with me somebody can have a copy of I was going to read it out but I guess we haven't
we're going to do this so one of the things we're going to learn this is not one of my big General ideas that isn't a
bad one one of things we should learn is when you have a difficult problem like this it's a good idea to try to break it
down into some smaller problems because the whole problem just seems unmanageable so what I'm going to do is
I'm going to break it down into two pieces see if we can figure out what to do in two kind of easy pieces and then
use those pieces as building building blocks to try and get the general answer okay that's going to be my strategy here
all right so the first building block uh we'll call it a building block a and building block a
going to assume I don't write this bit I'm going to assume that no one has shot yet all right so assuming no one has I
not shoot or throw if you prefer uh next turn can I use the word tomorrow for next turn it'll save it save us having
to write next turn every time we we we will not shoot tomorrow when it's player J's
turn then what so your player I let's say you're Robert and you've got your sponge and James still has his sponge
and it's your turn and for some reason you know you Robert know that James is not going to throw next turn assuming
that no one's throwing it should you throw now or not no you should not throw right you should not throw why should
you not throw now in that second you got a better chance next time right because if you knew that the other guy is not
going to shoot next turn tomorrow then you're going to get a better shot The Day After Tomorrow doesn't mean you
should necessarily shoot the day after tomorrow but you're certainly shooting the day after tomorrow is better than
shooting now is that right everyone okay with that this this this is meant to be the easy fact let's make sure this one's
this this is good y so if I know the other person's not going to shoot tomorrow I should not shoot now I should
wait till the day after tomorrow we're good David we're good on that okay I'm checking because he's my teacher all
fact B you can kind of guess what it's going to say it's going to say assuming no one has shot
tomorrow same thing with Will with Will with will not replacing will right so again suppose you're Robert no one shut
the sponge yet no one's thrown the sponge and you for whatever reason you know that if you don't shoot now James
on okay so we're getting better than that depends on distance and the reason it depends on distance it depends on the
probabilities and it indeed depends on who's the better shot all right so it's going to depend on all those things can
we be more precise so that's right it it does depend on distance it depends on distance because the probabilities
depend on distance and the prob is themselves depend on who's a better shot so it's right it depends on those things
misses so second again he's an engineer doesn't shouldn't allow the engineers here that's right so
okay so here here's the answer that's right so so what do you have to compare you have to Jo yeah go
ahead true that that's a good point actually but but notice I've assumed I've assumed that I've done that here so
the assumption that you know these curves means you really do know what these probabilities are so in some sense
even we didn't play it that way we've assumed that you know the weight of the sponge so so here's our difference
between reality and the Assumption so in reality James probably doesn't know his own ability or the weight of the sponge
but we're going to assume for today that he does just to keep things simple all right so let's let's come back to that
it depends again so what does it depend on if I throw now's State the question again before I answer it the question is
if no one has thrown yet and if I know that you are going to throw tomorrow if I don't throw today sorry I know that
you are going to throw tomorrow if I don't throw today what should I do that's was the question and the answer
is it depends and they then it's what does it depend on well what do we need to compare we need to
compare what happens if I throw if I throw then my probability of winning the game is the probability that I hit the
at me tomorrow then my probability of winning the game is the probability that he misses tomorrow is that right so I
have to compare the probability of my hitting if I throw today with the probability of him missing if I leave it
and let him throw tomorrow that make sense right compare apples with apples or oranges with oranges so the answer is
Pi d That's the probability that I hit if I throw today is uh bigger we'll make it bigger
than equal let's not worry about the equals for now doesn't really matter so we make it bigger than equals as for
today uh uh p is greater than equal two the probability that he misses tomorrow and that's 1
the probity that I hit today if I if I shoot and this is the probability that if I wait if I don't shoot and he then
shoots at me this is the probability that he misses tomorrow am okay that one minus makes it the probability of him
missing and D minus one because we're closer together tomorrow all right everyone okay with that yeah somebody
can wave if they're not it's okay it's okay to should I do it again Jo good good
again yes on okay so this is the probability of winning by my hitting and this is the probability of me winning by
his missing okay now I'm actually going to do some real math and I know that some of you are not you know didn't
excel in math in college and pretty math nervous so this is the only actual math I'm going to do uh so those people are
nervous can you please hold on to your seats underneath the cushions just for a second I'm going to add uh I'm going to
add p J D minus one to both sides of this thing all right okay is that's the only math I'm going to do here okay okay
minus1 is greater than equal to one okay everyone okay with that bit of math I just added something to both sides of an
inequality yeah I know the physicists are okay with that I mean everyone else going to be hard to see in the last is
let's can people Charles can Charles can you see that up it need to be higher okay we're going to raise it
is Char okay yeah okay all right so what do we know now we know what you should do if you know the other person's
not going to shoot that is to say you should step and we know what you should do if you know the other person is going
to shoot which is you should shoot if and only if this sum is bigger than one let's go back to our picture let's put
some steps in so these are very little steps because it's a very little picture I'm
I'm not insulting the foot size of the Deans it's just you know I've scaled it down okay and uh let's see where would
okay so at the beginning of the game when people are out here if we ask the question is P or p1d at the beginning P
p1d plus P2 2 D minus one is it bigger than one is it bigger than one out here no it's small these are two small thing
so it's it's going to be smaller than one on the other hand once we're in here once we're in really close the sum of
these two probabilities is bigger than one okay everyone okay with that and there's going to be a critical point
when for the first time the inequality switches from being incorrect to correct from being false to being true all right
it approximately here but pretend it pretend it's accurate right so what are we saying here we're saying this
inequality which I'm claiming is going to be important but none of you know why yet I'm claiming is important this
inequality is not met not met not met not met not met not met not met not met not met and then it's met met okay okay
good so now let's CL make a claim and then prove the claim so I claim that the following is
true I claim that nobody should throw their sponge until D star but whoever's turn it is at D star
next person should throw at D starus minus one okay so so here's my claim nobody throws before D but at D St you
throw whoever it is okay that's what we're going to try and convince you try and convince you that that's true all
right to convince you that this is true we're going to use these two facts and these two stooges all right so so
I'm going to bring my Stooges up again and convince them we're going to if this was ESPN we would be playing
things in slow-mo I don't have actually in the drama school they probably have that but
I don't have slow-mo in here so we're going to play slow-mo in kind of uh imagine slowmo here we are back back at
the beginning of the game and we're going to do slow-mo and here we are who first I forgotten so James was first
he's player one and he is thinking what should he do should he throw or step now we know the answer but let's
just walk through it slowly all right so James can think the following way suppose suppose Robert was not going to
throw next go suppose it's the case that Robert is not going to throw next go then which fact should he use should he
use fact fact a or fact B A and what would his conclusion beep step okay that's one thing that Robert could think
uh so one thing that James could think but the other thing James could think is he could think suppose Robert is going
to throw next turn right so if James thinks that Robert is going to throw next turn then he should use fact B and
the conclusion should be well he if he's using fact B James should throw if his James's probability today plus Robert's
probability tomorrow there it is I've just draw those lines is bigger than one is it bigger than one no so he should
step so in this case whether James thinks that Robert is going to throw tomorrow or thinks that Robert is not
going to throw tomorrow you arrive at the same conclusion namely you should step and therefore you should
step okay so all right all right so let's do this once more in Robert's shoes but you'll see the same idea so
I'll do it faster I can speak fast uh here's Robert Robert is thinking what James is going to do if Robert thinks
that James is not going to throw tomorrow then by fact a Robert should step and if Robert thinks that James is
going to throw tomorrow then should use fact B and look at these lines on here and say Throw if this line plus this
line is bigger than one but they're not bigger than one they're smaller than one and therefore either way he should step
so he should step okay everyone okay with that argument okay okay so just I I promise I'd point out some things I'm
going along that are more General lessons right so the thing we just saw was an example of what's called a
dominance argument a dominance argument says if I think a if I think I don't use a if I think P then I should do X and if
I think not P then I should do X therefore I should do X all right dominance arguments pretty
straightforward but people get them wrong okay so so if if you do the same thing whether P or not p is true then
you should do that thing okay if I had time I'd give you examples of movies where they don't do it but never mind
okay so all right so fine so so Robert should step and then James will go through the same argument it'll still be
a dominance argument so he should step and then Robert should step we're going to go in fast motion for a second uh and
this will go on being true until we get to about here come come come come come come come stop okay okay so here they
are so we're going to get so we're going to get uh not shoot not shoot not shoot not shoot not shoot not shoot not shoot
not shoot not shoot not shoot so uh let's see two one two one two uh so uh uh here we are finally at D start all
the way through this argument including the last step which was which was uh James's argument at D Star Plus One the
dominance argument said no matter what I think I should step so I step now however we arrive at Dar and here's
here we are we're in Robert's head this is a good head to be it I i' read some of stuff so managing yourself in
Robert's head and Robert is is putting himself in James's head trying to think this through and Robert is saying if I
think that James is not going to shoot tomorrow then I should use fact a and that tells me not to shoot
today but if I think that James is going to shoot tomorrow then I should use fact B and this time for the first time when
I work my way through fact B it tells me I should shoot today right because I'm at D star so now these two arguments are
pulling in opposite directions if I think the other guy isn't going to shoot I should step if I think the guy is
going to shoot uh then I should shoot so I'm stuck I'm stuck all right so it was easy up to now we had don't shoot but
now we're at D star now if Game Theory could say nothing other than these dominance arguments you probably
shouldn't take my course all right so it better be the case I've got some way out of this dilemma this is a dilemma but I
way out of it so here's here's how we're going to get out of this D we're going to figure out remember we're in Robert's
head all right echo in there right we're in right here we are it's like a church right so in Robert's head we're going to
try and remember this dilemma would be solved if Robert knew what James was going to do tomorrow so we're going to
work out what James is going to do tomorrow but we're not going to do it as was suggested just now uh uh by by by Mr
Mor by just taking one step forward we're going to take lots of Step forwards in fact we're going to go to
the end of the game so what's the end of the game The Last possible step in the game so come forward come forward no one
shoots no one come come come on personal space but further forward all right okay all right so this is the end of the game
all right no one shoots no one shoots no shoots eventually they're on top of each other their noses are touching it's
uncomfortable all right all right okay and here we are at the end of the game and this turns out to be
Robert's Turners again and so if Robert finds himself at distance Zero from James if we get here what should Robert
do sorry yeah what should Robert do he should shoot why should he shoot because he's going to hit with probability one
so he should shoot is that right all right so that was easy so if we get to this stage Robert's going to shoot let's
go one stage back in time no no no no it was must have been his turn it's your turn now so the previous turn must have
been James's so James is going to go back in time okay so here we are one now we the distance one apart by the way we
had a shoot here right can now their distance one apart and it's James's turn and now
what does James know that Robert's going to do tomorrow if James doesn't shoot he knows we just put it on the picture he
knows that Robert is going to shoot and therefore James should shoot he should make that decision based on fact B is
that right James knows Robert's going to shoot tomorrow so James should shoot if his probability of hitting now plus
Robert's probability of Tomorrow is bigger than one and since Robert's property on his own is one for sure one
plus something is bigger than one that was another second bit of math I lied okay there two bits of math in the
course right so one plus something is bigger than one so he should shoot is that right right so so James you would
shoot at this point right all right so so now let's go back one more stage so now so here we are now we're at stage
two two away all right and now we're in Robert's head and what does Robert know what does
Robert know he'll shoot he'll shoot and therefore what should you do shoot right because why why should you shoot because
you go through fact B and you find the some of the prob is bigger than one so he should shoot so let's go back to
uh uh three which is actually our D star minus one here's James this is what we were worrying about right right so what
does James know at distance three what have we just worked out he knows that James knows that Robert's going to shoot
and so James should use fact B and using fact B he should he should shoot okay so now let's
go back one more stage and now we're back where we were where our dilemma was now we're back at D I've worked my way
back to DAR and but what's difference now now when I arrive at Dar from the end remember last time I was at D star I
had a dilemma in Robert's head because I didn't know whether James was going to shoot or not but now I do know what he's
going to do what's he going to do and therefore what should you do there we go so we've just we've just shown we've
shown that at D star Robert shoot in fact what have we shown we've shown until D nobody should shoot but at D and
if you get there any stage afterwards you should shoot all right so thank you to my my two doas again sit them down
again thank you you can go just seat thank you all right thank you you expect them to be great actors
and great interpreters of the law so that's that's good this is the the law of Game Theory all right so what did we
that what I claimed we showed that no shot should occur until D and that at D which of course depends on people's
abilities but at the star whoever's turn that happens to be should shoot and we use two big Ideas I didn't point out the
second one so I forgot so I'm going to do do so now the first big idea was this dominance idea and the dominance idea
was if you if if in circumstance P you should do X and if in circumstance not p you should do X then you should do X
right I'm saying that adamantly because it seems obvious right and that was one big idea and the other big idea was when
you get stuck in this thinking this way a really good way to solve out a game is to go to the end of the game and work
backwards right it's good to anticipate what people are going to do and the best way to do that is to go to the very end
of the game and then work yourself back forward again all right now that idea is called backward induction backward
induction and backward induction is the most important thing you're going to learn if you take a game through class
it's hard to do actually it's hard to do because it's hard to make yourself do it it's hard to have the Instinct that I
really should work backwards and not forwards time works forward right our logical way of thinking works for
forward but when you're trying to play a game with somebody trying to put yourself in other people's shoes whether
putting yourself in your shoes TR to anticipate what they're going to do while they're anticipating what you're
going to do it's easier to work backwards so backward induction combined with dominance tells us when we should
understand the game before we draw out any more General lessons people okay at this point have I you don't particularly
look like deer in the headlamps which is a good sign say I haven't lost too many of you is that right good okay
so yeah it always happen that when you get stuck that if you reason from the other end yes yes it's because if you
look at those inequalities it's monotone so I'll show you after but basically as you get closer both people's
probabilities are getting higher always so that pair of probabilities you're always you're always going to cross one
out and replace it one of them will survive and the other one get will will be crossed out with something bigger so
once you cross D star once you cross this inequality you can't go back it's it's it's it's it's a strictly mon
sequence that was a physicist asking the question so I assume I answer is in the appropriate language okay all right good
better shot shoot first or should the worst shot shoot first and it isn't even a question of preemption and preempting
preemption it's a question of understanding both probabilities working the thing backwards and finding out that
there's a critical moment to shoot now be careful here I'm not saying that that critical moment to shoot doesn't depend
on abilities it does depend on abilities so it's very tempting to say look a critical point to shoot here and this
corresponds to when you see the white in the other person's eyes not quite true right CU you know when you see the whes
in other person's eyes depends on your eyesight and when you should shoot depends on both your abilities right so
so I'm not saying there's a unique time to shoot but I am saying it isn't a question of who the best shot is it's a
question of both abilities put together now let's throw in some dust let's make this harder all right so we now all know
that if you're playing this game you should shoot at D if you knew everything you knew and if you taken the course but
you might say that's fine but in in it's fine if I'm reasoning I'm playing this game against another person who's in the
room who's taken the course but what if I'm taking the what am I'm playing this game you know it's life and death it's
it's nen and lsky uh neither of them took the game three class it's as far as I know they didn't take the game three
class I'm looking around for a Russian scholar I see a German scholar but not a Russian score so but as far as I know
they hadn't taken a game three class before the beginning of a all right so and you might might think what if I'm
playing against somebody who's a little crazy right so what if I'm playing against a crazy person right I could be
I may have gone to Yale but I could be playing against somebody who went to Harvard right who who never had a chance
to take a decent game three class and so so um how would it how would it change our argument if I thought the other
person was a little crazy let's still assume that we know each other's abilities but now I suspect the other
person just isn't capable of reasoning through in the way we just did how does that change the argument would
think good good so even if you're playing against a crazy person even if you're not confident in the other
person's rationality or even not confident in the other person's confidence in your rationality or any
other statement of that form which is often true in the real world even in that circumstance where you don't know
you're playing against a sophisticated person it doesn't change the argument it doesn't change the argument in here it
doesn't change this argument and it doesn't change that argument because that argument was a
dominance argument that argument said I don't care who I'm playing against whether I'm playing against a Yale
student or a Harvard student I don't really care if the person's human right the person could be a Ballard for all I
care right all I care about is whatever is going to happen I should I should not shoot therefore I should not shoot right
that right so in in the first part of the argument the dominant part of the argument there was no interesting
thought of the form if the other guy is rational and if the other guy knows I'm rational like that it was just a
and I was kind of thinking that he can figure out that I'm rational or that he can figure out that I can figure out
that he's rational or she right so it's used he and it easier so uh in in this piece of the argument Robert at D Star
had to figure out what James was going to do at darar minus one and that argument required him to have confidence
that James would figure out what Robert would do at D star minus 2 etc etc etc so not did it require thinking the other
person putting myself in the other person's shoes and thinking they're rational it required putting myself in
the other person's shoes while they're putting themselves in my shoes and they know that I'm rational and so on so
forth right so the backward induction argument is much more um fragile to irrationality right so lorri sanis gave
a talk yesterday about irrationality which is an incredibly important topic these days you know it's possible that
on Monday they might give the Nobel Horizon economics to Robert sh which be very nice who's worked on on such topics
in finance irrationality here doesn't affect this part of the argument it does affect this part of the argument all
right now nevertheless nevertheless the fact you should not shoot before here is a pretty strong argument right because
frankly by the time you figured out the other guys's irrational it's too late you don't really care if he shoots
early here you're perfectly happy if he shoots early here all right so this argument this particular example even if
I think the other guy isn't rational I shouldn't shoot before d now let's push that idea further I've
played this game in class with undergraduates I've played it in U my business school class with business
school students I've played it with parents I've played it with alumni I've played it with
Deans uh and uh uh so I have some idea about how people do on average in this game now assuming that people are
following the reasoning I just said and assuming that ability is distributed roughly randomly and also making this
somewhat unreal assumption that people know each other's opposes how often should I how often do I expect to people
person shooting it could be the stronger person shooting if it's happening at D star one is uh the sum is one all right
so what's on average on average how many hits should I see 50% right so if I get a large enough sample there's a bit of
hand waving in that argument someone was going to point out allowing me a little bit of hand waving right for discreet
versus continuous roughly speaking 50% should hit I see far fewer than 50% massively fewer than 50% I would say I
see 10% hits why why do I see 10% hits when the when we just agreed that even if everyone's crazy and irrational no
one should shoot between before D star and D star is telling us that half half the shots should be hits why do I see
although that might make them shoot later I mean you know in some sense right so I think there's two
things going on let me take them in turns this one first overestimate so I think I think people do two things they
they overestimate their opponent they also overestimate their own abilities all right so there's a well-known
psychological bias that people overestimate their own ability to do something they probably also
overestimate the other person but they certainly overestimate their own ability things so there's an overconfidence bias
and there's stacks of literature on the overconfidence bias right so if you if you Google overconfidence and start
reading papers you can be there a long time right so it's pretty well established that people are
overconfident in their abilities amateur golfers will try that shot which they've seen Tiger Woods do where he slices it
between the trees right and I don't play golf but I'm told amate golfers are never going to hit that sh all
right uh I don't actually I don't know the answer to that Meg it's possible um uh there probably is a literature on
that because almost all these things have been tried uh uh uh with uh gender in there uh if I had to has a guess I
would say men are more over confident but I don't know the data so I without seeing the data I I have the same
suspicion you have so one thing is overom that's a well-known bias I think there's another
thing going on here and I think it's going on specifically in America and I think is is what's going on is another
thing going on here I think that at least in America there is a thing I want to call the proactive bias right people
like to be proactive when your kids in America you are taught that being proactive is a good thing I know this
because I have kids I have a 10-year-old and an eight-year-old I have a one-year-old too but he hasn't gone to
school yet my 10-year-old and my eight-year-old both of whom are girls are being told uh uh being proactive is
good seizing the bull by the horns is good I also have more evidence about this so just to make it clear being
proactive would be throwing the sponge rather than letting things happen to you right so people think being proactive is
good and you see this on on Sports Center for those people watch sports center you'll see these guys in the
sweaty um usually it's guys it could be actually I don't want to be sexist about this think it's males or females they're
in this s sweaty locker room afterwards and they make this statement and they say uh it's great because we control our
own destiny and coming from England controlling my own destiny just kind sounds kind of scary to me
causes people to throw the sponge too early right that that taking the bull by the horns sounds like a good idea but
when you think about it running away is an awfully better idea right right so uh if I have one last lesson for you other
than you know the takeaway lessons from today's today's talk go through them one is dominance
arguments I won't R what they are the second is backward induction sometimes it's worth going to the end of the game
and working backwards and the third is this and it's really just for the Americans I think the Europeans in the
room don't make this mistake and that is this the point is not to go down swinging the point is not to go
but I want to make sure you get me make it to the next talk so I won games I have solved completely if the opponent
it on his head the question yeah so the question was what if you're playing against Gandy right so gandi is not
going to shoot you cuz he's a saint so if you're were going to win the game and you are so inclined and Shan is a
cical kind of guy he just wait and plunk the sponge on Candy's head an image I'm now going to have when I go to bed
tonight do I like the casino I never go to a casino um um um I yeah I don't really like Ian out of interest I'm not
a big Casino Player I kind of like playing cards casino I mean roulette wheels seem a little bit too random to
21 Blackjack thank you and and and it turns out that people do exactly the wrong thing there uh they they uh um
what do they do uh they um they quit when they're behind uh rather than quitting when they're ahead and it turns
out since you since you use five packs and so random sample if you've been doing well you know any sensible
updating will say you're going to do worse in the future and if you're doing badly you're actually going to do better
there's actually a regression to the mean so people do exactly the wrong thing and I'm scared I would do the
nature yes it's a good question it's a very good question so the question is can we
see games like this in nature so let me as as like a politician let me answer a slightly different question we come back
so so so uh game theory is enormously used now in biology in in behavioral biology it's it's a major tool and uh it
turns out that there are wonderful connections between the game theory we developed in economics uh and Notions of
equilibrium in economics and Notions of evolutionary stability in in in in uh in biology and uh they're not exactly the
same idea but one is kind of a sub of the other and uh what you can do uh in evolution biology which is kind of cool
is if you if you know the basic form of a game that a particular uh species is playing be careful because the actors
now aren't rational they're it's Gene selection but still if you know the form of the game but you don't know the exact
payoffs of the game you can actually uh look at the behavior look at the behaviors you see in the population and
back out what the exact payoffs must be which is a lovely example example of what's called identification in
economics right so so biologists do incredibly cool things with Game Theory actually at this point they do cooler
things than frankly economists do with game three it's really cool now this particular game I don't know there's
some biologist in the room I'm looking at Tom I I don't know exactly what game this would correspond to in nature but
there are games that uh a better example for nature is the game rock paper scissors and the rock rock paper
scissors so rock paper scissors everyone know that game rock paper so rock beats uh scissors and scissors beats paper and
paper beats rock that game right so rock paper scissors is a nice little zeros some game that you can find examples of
that look a lot like that in nature and you can twiddle them a little bit so not exactly Rock pus is and they actually
have no evolutionary stable uh point and you can show in examples of that uh Cycles occurring in in populations of
actually the most famous example is uh uh tree lizards uh and meeting behavior of tree lizards and you can show you can
predict out from those Cycles what the exact payoffs of the rock paper scissors game they were playing was so you can do
really cool things in biology with this but Tom knows more about that than I do so I'm going to I'm going to I'm on
day-to-day work as a Provost I I um yeah so it's a good question so I I I I do a little bit I mean I think I think
I've been doing this so long that it's kind of hardwired for me to think this way so I do tend to lay out things and
kind of work them backwards and I do tend to sort of try to go down one branch of the tree at a time and see if
they're all the same if there's a dominance argument there I can see a hold of but also a large piece of Game
Theory as applied to economics or to organizational behavior is the theory of incentives and as you well know Tom is
the dean of the graduate school he's a wonderful dean of the graduate school and he steers the graduates in a
wonderful way uh some of that is about incentives that's the game theory part and some of it is
about your relationship with the grad students which is more the psychology part so I'd say Peter and I have the
combined have the skills but Peter has the more important skill from me and well in this example you use you
know the shape of the the skill curve that each play yeah but let's say I go in the game and I know my skill curve
but I don't know my opponents now my opponent may have a average skill curve may have a highly skill curve may have
skill curve right how do I develop a strategy good good so so it's it's harder but not impossible so it's harder
because now we'd have to think about the population of skill curves out there and I I I want to be a to think of my
opponent as being drawn perhaps randomly drawn from some population of skill curves and uh so I'm going to have some
I'm going to index each skill curve and I'm going to take I'm basically going to take expectation at every point in the
game over those skill curves so essentially the reason I didn't do it here is I need to carry a whole bunch of
integrals and I'm taking I'm taking distributions over curves which is a messy thing to try and do but basically
the basic idea is still the same I'm there's going to be I'm going to be carry some expectations around uh
because now I'm not now it isn't that I know what the probability of this guy hitting tomorrow is it's that I I I know
only the expectation of that I know with expectation what that what their probability of hitting is if they were
to shoot tomorrow uh so that means that the math is a little harder but the basic idea of looking forward and
working it out is still runs through I I'm I'm underselling the math a little bit uh because not only do have to worry
about the distribution of the distribution of skills out there and worry about taking expectation over
those skills but that distribution is going to change as the game progresses I'm going to be able to infer from the
fact that the guy hasn't shot yet that he's not a skilled as I thought he might be right so that distribution you think
about some bell-shaped distribution of skills where these are the High skills and these are the low skills some of
those High skills are going to I'm going to be able to conclude that they're not in the game as the game proceeds when I
see the guy not shoot so I have to but so I have to keep track of all that stuff I have to do B in updating on this
distribution I have to get some expectation and so on but up to a lot of kind of math nice math but out of math
the basic reasoning still goes through that's so so the reason I didn't do it here is you can kind of hear there's a
lot more math involved but it's going to be okay well doesn't it change if if it's a life or death game my objective
is don't lose that's let and it great if you don't win it yeah so so doesn't that change my my it
actually so that's an interesting point so so in this example if there's just two monetary prizes one for winning and
one for losing and the winning one is strictly better than the losing one then it actually doesn't change the strategy
in in in this simple game but but that's too quick an answer imagine there's three outcomes imagine there's an
outcome uh so imagine the game is not is being played not exactly as we played it with sequential moves but with
simultaneous moves right so in each period people simultaneously have to decide whether throw or not right so now
a third outcome is in the game now there's the outcome win there the outcome lose and there's also the
outcome both Miss tie or Draw right now now it's more complicated why is it more complicated because when there are three
outcomes we have to take into account things like risk aversion just as we would the many money outcomes if there's
only two monetary outcomes or two outcomes this analysis is fine but as soon as we go from two to three we have
to start worrying about risk aversion and things like it again kind of in David's territory we have to do a little
bit of of what David does for a living to solve those things but it's it's a great question yeah proba make this the
last question because you have other talks to go to but sh distinguishes among three levels
sociologist now as you can hear so uh I agree with that so so by the way today was high church because well look around
you so uh so what are we thinking so so so what we're doing in in mathematical economics or the more mathy end of the
social sciences is trying to tease out our intuitions and trying to tease out how different assumptions lead to
this is a tight prediction of what's going to happen some things will be pretty robust this this argument about
dominance is pretty robust right but most arguments are not that robust and one of the things we have to do in in in
in most areas of theoretic economics but the same is true in theoretical areas of sociology is we need to tease out
exactly what are the assumptions we're making and would these results be robust to changing them so the great thing that
and this is not the most inspiring things to end on but I'll end on it despite that the Great thing about doing
mathematical social sciences which I I guess is what I've done in my career is is it allows you to think through a kind
of thought experiment rather than experiment it says I can't really um so I'll be having some discussion let's say
with my wife who's an English professor and she'll say yes but you've assumed this this and this and it allows me to
say okay you're right all those I did assume this this and this a b and c but look the argument still works if I drop
assumption a the argument switch is exactly at this point if I drop assumption B and if I drop assumption c
yeah you're right the whole thing's completely nonsense right that's a great conversation for uh scientists and
humanists or in this case social scientists and humanists to be having it shouldn't be a hostile discussion it's a
discussion about focusing in on the details of an argument it's a great Yale scholarly thing to be doing and Martin
schik did it much better than I ever will he's a Yale Professor one of the founders of Game Theory there are many
people around Yale doing things better better at that than I will but you have a chance to see some of more some some
more of them later on this afternoon so thank you for coming uh and we'll see you later on this afternoon thank you
Heads up!
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