
Why I give my students a ‘tragedy of the commons’ extra credit challenge - nkurz
https://www.washingtonpost.com/posteverything/wp/2015/07/20/why-i-give-my-students-a-tragedy-of-the-commons-extra-credit-challenge/
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paulsutter
The professor omitted the sole interesting number: what percentage of students
choose 6 points. Is it typically 15% or is it typically 80%?

It makes a huge difference. Most likely, it's a percentage low enough to
indicate that the 10% threshold is carefully chosen. Otherwise he'd tell us.

This is evidence that he has an agenda to promote (that people are too
selfish), and that the facts don't support his agenda (most people actually
cooperate). So he omits the facts.

~~~
bduerst
Or maybe it's 70% of the students who pick 6. Or 99%. Or maybe 10.01%.

The point is we don't know and can only speculate, just like the students in
the experiment who don't have the signal either. It kind of sounds like you
want to believe the professor has a bias, and are trying to speculate evidence
to support that belief. Even in the article he talks about how picking 6 in
the first round isn't viewed as selfish, just that this experiment
demonstrates tragedy of the commons.

------
fcbrooklyn
Actually, I think in this case the only rational choice is to ask for the 6
points. One of two things will happen:

1) Less than 10% will follow suit, in which case you'll get a 6 point boost,
and you'll have secured an advantage over 90% of your classmates.

2) More than 10% will follow suit, and noone will get anything, in which case
you will have no advantage over your classmates, and neither will any
classmate have an advantage over you.

If you select 2 points, then either:

1) Less than 10% will opt for 6, in which case you'll have no advantage over
at least 90% of the class, but some members of class may have a 4 point
advantage over you, or

2) More than 10% will opt for 6, in which case the outcome is identical to
choosing 6 in the first place.

Because the "points" have no intrinsic value except in comparison to your
classmates (unlike a true tragedy of the commons, where the scarce resource
such as food, etc, has real value), there is no reason not to roll the dice.

EDIT: Many people think the fact that the course is "not graded on a curve"
makes a difference. It does not, at least considering the class in isolation.
I took courses in college where an A was pretty much a dead certainty, and
other courses where getting a B was actually quite an achievement. In all
cases my performance within a course had to be judged based on my performance
against the other students within that same class.

~~~
edwardy20
> Because the "points" have no intrinsic value except in comparison to your
> classmates

This is where your logic is wrong. The professor is not saying the class is
graded on a relative scale (for example, top 10% of the class gets As). If
everyone gets two points, and it bumps up everyone's GPAs, then of course it
will benefit them all, especially in comparison to people who are not in the
class.

~~~
gorena
This is not necessarily true. If you're _already_ a good student, this
devalues your GPA, mostly due to the generally awful GPA system. Assuming your
school considers everything above a 92 to be a "4.0", if you're already in
that range, you definitely don't want to help anyone else into that range.

Note that, of course, this would be fixed by just making GPAs decimal numbers
out of 100, the average of all of your _actual, numeric_ grades from each
course (multiplied by credit hours?). You can divide it by 25 if you really
want the weird 4.0 scale for some reason.

------
Tossrock
It's funny how many people are saying "oh just get everyone organized and have
a lottery/auction". Yes, if we could perfectly organize large groups of people
we could solve the tragedy of the commons. Unfortunately, organizing large
groups of people is hard.

Even in the scenario where everyone is a rational actor (ie, fantasyland),
effectively communicating to a group of > 20 people and obtaining unanimous
consent is an exceedingly difficult problem.

~~~
bduerst
The anonymous nature of this removes the reputation cost for picking the six
points.

Collusion isn't possible because there is no penalty for breaking an
agreement, and the signals it creates (everyone is picking 2) only makes
rationally self-motivated individuals more likely to break it.

------
andresmanz
> I’ve been giving it to students since 2008, and only one class has
> successfully mastered the challenge.

That's a real surprise. The 2 points option is the safe one, so everyone
should go with that. Sure, I could assume that all (or most) of the other
students think so and just get the 6 points myself. But then again, chances
are that the other students think the same. So let's just go with the safer 2
points.

~~~
justonepost
No, the safe option is to get organized and plan out who is going to chose the
6 points. That way, you know if you secretly chose the 6 points when you were
supposed to get 2, you will get nothing. Then it doesn't become tragedy of
commons, but rather an experiment with vandalism.

The experiment, IMO, isn't valid. In RL tragedy of commons, the selfish don't
really suffer that much .. it's usually everyone else that does.

~~~
scottfr
You could have an auction for the 6 point slots, with the proceeds being
divided and distributed to the group.

~~~
dogecoinbase
I was going to respond to the GP that you'd likely have a spoiler who would
either be upset at not getting the six points and so secretly blow it up, or
demand to be one of the six-pointers by publicly threatening to do so, but if
there's money involved than that "likely" turns into a "definitely".

~~~
protomyth
I don't think you would have a spoiler, or someone who pulls the demand. I
think the money would actually stop that pretty quickly because of the peer
pressure ramifications from the others in the class.

So, a 20 person class has 2 6pt slots. You take the bids and collect and hold
the money. Grades are announced and then you hand out the money or give it
back to the original bidders in case of betrayal. The spoiler is basically
denying the points and cash to everyone. I get the feeling the identity of the
spoiler would be found, if for no other reason all the innocent folks showing
their papers. I hope the spoiler is graduating and not coming back because
that type of crap is remembered.

------
hcurtiss
Cooperative behavior is particularly difficult when the stakes are very high.
In the context of climate change, increased energy costs have very real
impacts on people day to day, particularly in developing countries. For this
reason, it's difficult to imagine those countries would behave cooperatively
(even if a figurehead signs a document promising they will). It may be that
the better strategy is to have the best grades in the first instance, knowing
that noone will get extra credit. That is, build a strong and resilient
economy so that you are better prepared to deal with, and adapt to, the
inevitable challenges associated with global climate change.

------
TimPC
I think this would be more interesting if there was a way to explicitly
declare the marks post-curve. In the event the distribution of marks is
smoothed to any sort of typically college distribution it's entirely rational
to just select 6 points and not care whether 10% of the others do or not.
Selecting 2 leaves you open to a worse result on a curve, but selecting 6 is
nearly risk free if the distribution of marks is precisely controlled anyway.
2 marks when the average pre-curve goes up more than 2 and the average needs
to be fixed post-curve is a really crappy proposition.

~~~
warkdarrior
The article specifically state that the grades are not curved.

------
xg15
I wonder if jealously could also play a role here. The option to choose 2
points doesn't seem completely risk-free to me from an "emotional" point of
view:

Suppose you choose the 2 and the class was actually disciplined enough that
the points weren't lost. Then you might think that there might very well be a
small group of students who got 6 additional points because they were greedy
and you were not.

If students underestimate the risk of all points getting lost, they might in
turn overestimate the "risk" of getting less than others if they play it safe.

~~~
haberman
Congratulations, you just independently discovered the sixth paragraph of the
article!

"But many students choose the seemingly selfish option. Why? Perhaps to
increase their own grades, or perhaps because they fear that they will be
taken advantage of. No one wants to be the chump that chooses fewer points
when they could have had more."

------
jedmeyers
Get together, auction the 6 point slots. Then, depending on whether it works
or not, either evenly distribute proceeds to everyone or return the money to
the auction winners.

~~~
ryan-c
Or more generally allocate the 6 point slots in advance - how they're
allocated doesn't really matter. The point is that everyone knows that if they
are supposed to choose 2 points and instead choose 6, nobody gets anything.
Someone still might blow it for everyone out of spite, though.

~~~
jedmeyers
By involving the auction you are adding an additional incentive to not blow it
for everyone - you are getting money from the person who will get higher extra
grade than you.

------
pitt1980
I wonder if the prof has given any thought to what made that one class unique,
if there were any factors that distinguished it from his other classes

off the top of my head, I wonder if it was a particularly small class

though I could imagine a lot of other potentially relevant factors

------
bsder
This really doesn't work for me as an experiment.

10% is too easy to hit. Do 3 or more students _need_ the 6 rather than the 2?
Why should I choose the 2 if it won't do me any good?

In any class I teach, there are generally 10% on the line between grades that
requires that I take into account a little more than just scores. Did they do
all the homework? Did they improve on assignments or were they blowing them
off? etc.

Given that 10% probably _need_ the 6 and not the 2, this is likely to never
work.

I had a tragedy of the commons that I hadn't intended. I had an extra credit
programming assignment, but there was a catch--the _students_ had to write the
tests for the automated tester. If nobody wrote tests, nobody had the chance
to get any extra credit. They were allowed to collaborate on the tests, but
not the solution.

Everybody complained bitterly when nobody wrote tests.

My response was not terribly charitable: "This is _extra credit_ , folks. Not
charity. You all had two options.

First, write the tests yourself. Yes, writing tests is time consuming, but not
horribly difficult. Some students started, realized the amount of work, and
stopped. However, once _somebody_ writes the tests, everybody get to benefit.

Second, _encourage_ someone else to write the tests for you. Did any of you
_talk_ to the students most likely to write tests? Did any of you encourage
these students to put in the work if you couldn't pull it off yourself? Did
any of you offer to compensate them for their valuable time?

Many of you have been repeatedly asking for a group assignment since the
beginning of the semester. THIS WAS A GROUP ASSIGNMENT AND YOU FAILED. It
simply worked out that freeloaders weren't _guaranteed_ to be carried by the
best students. The best students realized the amount of work and simply opted
out since they already had enough points.

Welcome to the real world. Figuring out how to get someone to do something
that they don't really want to do is a fundamental problem of life."

------
sosuke
But the challenge doesn't make sense, there isn't much risk, no fear of being
known. Economic studies have covered this before, would you rather make $50k
where everyone else makes $75k? or make $40k where everyone else makes $30k
and people pick the latter because they want to have more than their peers.
Everyone getting the same points doesn't change anything relative to those
around me.

In a paper score, assuming 100, 2 to 6 points just doesn't mean much. 6 points
is greater than 5, it could take me from 84 to 90! I'll go for the gusto and
try for 6. 2 points just doesn't make any difference, and I wouldn't feel any
better getting 2 points.

~~~
hcurtiss
Agreed, but your assumption may not be correct.

~~~
sosuke
You're right I vaguely remember seeing a very wide range of top scores
possible. From 25 - 200

------
hwita
Sure, the course grades are not curved, but the students are definitely
competing academically, especially those in the same class. There's class
rank, honors status, merit scholarships, internships, job opportunities, etc.,
that are technically at stake. It makes sense to choose 6 every time.

------
Smushman
I see it as a simple equation. I don't think it says more than that about
people.

Can someone enlighten me as to why a 90% break point? Why not for example 50%?
Is it because 90% introduces some level of collaboration or vice versa?

Sans collaboration or any other useful information (people I may already know
in the class, etc.), I would say at best you have a 50/50 chance of a total
stranger choosing the option that is better for the common good. That number
is based on it being college age students. If it were the general public at
large I would estimate at least 60% would choose the more personally
beneficial option.

Am I just extremely pessimistic? Please give your thoughts.

~~~
Amorymeltzer
I imagine it's because 10% kicks in really easy and requires the you to stop
and think about your actions. If you need a full 50%, screw it, go for 6,
almost everyone else will. At 10%, though, you stand a fairly good chance of
being the tipping point.

~~~
Smushman
With the given caveat that any more than 10% of the group requesting 6 voids
the whole thing, it seemed a foregone conclusion to expect 0 points. On the
off chance I am wrong about that, I would end up with 6.

So the final conclusion I had == highly likely 0, but a very small chance of
6.

2 points were statistically ruled out the moment I heard 10%.

I see how the thinking re: screw it though also is valid. Thanks.

------
tolmasky
Its funny because we see the tragedy of the commons "fail" (succeed?) all the
time in national elections: people are so afraid to "selfishly" choose the
candidate they actually want to win (and thus cause the opponent to win) that
we all "cooperate" on a sort-of ok choice (just like cooperating on 2 vs 6). I
guess that's argument for penalties.

------
tolmasky
I'm surprised no rich student ever just offered ahead of the tally that they'd
pay everyone $x if _no one_ choose 6, where x is more valuable than 4 points.
He now has the ability to safely choose 6, and everyone else is paid for their
cooperation.

~~~
drcross
Great, except votes are anonymous.

~~~
tolmasky
It doesn't matter because the requirement is NO ONE choose it. There is
nothing to gain by selecting 6. The second you are writing 6 down on your
paper, you better hope the 4 extra points are worth more to you than $x
because you have absolutely invalidated the game, not "maybe" invalidated it.

If x is big enough to trivialize 4 points, I am pretty sure no one would
choose it (or at least fell well below 10%). For example, if Richy Rich was in
your class and offered $1million to EVERYONE as long as NO ONE chose 2, I am
quite certain that even the most selfish actors would not write down 6. If he
offered 50 cents than I'm pretty sure some people would. Binary search and
you'll know how much a point costs.

(apologies if you commented before my edit)

~~~
s73v3r
Have I? Assuming that it's a large enough class to where there are at least a
handful of slots for 6s, and the one rich kid is offering the money so they
get the 6, I might choose 6 as well, betting that few enough people will
decide to risk it.

~~~
tolmasky
The whole point is that the rich kid is offering the reward solely if _no
other people_ choose the 6. NOT if its 10%. By choosing the 6, you necessarily
lose the money. Thus, you would only do that if the 6 points are more
important to you than the reward, since you will _absolutely_ lose the rich
kid's reward if you choose it.

~~~
s73v3r
But all votes are anonymous, so the rich kid wouldn't know.

------
acbart
Alternative experiment: every day, students are allowed to do this voting.
Assuming that the first few days run like this experiment, I wonder if we'll
see a change in their behavior. This actually models reality more closely, to
some extent.

------
MatthewWilkes
Perhaps it's just cultural differences, but nobody getting extra points sounds
like the most desirable outcome to me. Perhaps in a setting where the exam
doesn't count for anything it'd be okay, but it just seems so juvenile.

------
justifier
So you get all the grades from your fellow students and organise the bottom 9%
to choose 6 and the rest of the class chooses 2

in 6 months 4 points on a random test will be completely forgot.. might as
well game the professor that is trying to game you

------
jmmcd
The challenge was recently discussed on HN:
[https://news.ycombinator.com/item?id=9874215](https://news.ycombinator.com/item?id=9874215)

This new article is from the lecturer's point of view.

------
aaronchall
I suspect that professors aren't upset that the game theory is validated, but
rather they're upset that the students haven't done the analysis and thus
choose to change the game by introducing structural changes.

------
vm
"People conformed to the group’s positive behavior."

People are more likely to respond to social pressure, than to appeals to "do
the right thing." Valuable lesson for startup marketing... and maybe even
pricing.

------
theburg
Doesn't take into account the student's standing in the class. If I am
confident with the quality of my term paper and believe it is worthy of an A,
what do I care if I get additional points?

------
overpaidgoogler
Really odd that the professor does not mention carbon taxes in the story. It
doesn't make sense to borrow game theory from economics but completely ignore
the idea of taxing externalities

------
justonepost
Don't the students just get together and do a lottery? And in RL tragedy of
commons, it's rarely anonymous.

~~~
moistgorilla
And then one person says that they chose 6 points and haven't won it via
lottery. The other students can't retaliate because the only way to get back
at her would be to take away points from the entire group

~~~
6d0debc071
They can retaliate, there's simply a cost associated. That's one of the
reasons this is a poor exercise: In iterative games it's often worth making
sure people know that certain kinds of behaviour don't work - even where you
have to harm yourself in order to do so. Otherwise you'll always be held
hostage by those willing to move the costs closest in time.

I suspect this is why hatred and resentment are part of our make up.

------
zwrt
what if you choose 6 and explain to your classmates that "It feels good to be
cooperative both from a strategic and moral perspective" and the whole commons
thing and convince them to choose 2?

------
anti-shill
The commons worked great in two situations--1) europeans and 2) villages.

Maybe if we could get back to small villages of european descent we could have
a higher quality of life.

