7 ms·

Why I give my students a ‘tragedy of the commons’ extra credit challenge

66 points by nkurz 11y ago

hwita 11y ago
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.
justonepost 11y ago
Don't the students just get together and do a lottery? And in RL tragedy of commons, it's rarely anonymous.
- moistgorilla 11y ago
  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 11y ago
    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.
andresmanz 11y ago
> 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 11y ago
  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 11y ago
    You could have an auction for the 6 point slots, with the proceeds being divided and distributed to the group.
    - dogecoinbase 11y ago
      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 11y ago
        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.
        deleted 11y ago
        [deleted]
vm 11y ago
"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.
TimPC 11y ago
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 11y ago
  The article specifically state that the grades are not curved.
- cortesoft 11y ago
  It says in the very first paragraph of the article: "All selections are anonymous, and the course grades are not curved."
aaronchall 11y ago
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.
Smushman 11y ago
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 11y ago
  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 11y ago
    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.
- nadams 11y ago
  I think we are missing some context - and that is very important to show if the students could communicate/collaborate (such as a homework question) or a test question. > 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. It depends on factors such as the student's current grade. I would argue you are more likely to choose 6 if you have a lower grade. > If it were the general public at large I would estimate at least 60% would choose the more personally beneficial option. Here is an related experiment. Choose N random people, and offer 2 choices: $50 or $200 and run the same experiment. Here is an interesting question - are people less "greedy" if the prizes/points have a greater span? Such as instead of 2 points and 6 what about 2 points and 20 points. I think the experiment is interesting any way you think about it.
hcurtiss 11y ago
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.
pitt1980 11y ago
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
sosuke 11y ago
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 11y ago
  Agreed, but your assumption may not be correct.
  - sosuke 11y ago
    You're right I vaguely remember seeing a very wide range of top scores possible. From 25 - 200
- notahacker 11y ago
  To pick up on the point about positional goods, everyone failing the class actually improves the ranking of [up to] half the classmates. If the points count towards some total score and there's some kind of calculation to normalize grades across the student population, everyone failing the class might actually bump up the overall grades of some of the weaker students in that class. Conversely, in this situation nobody benefits from everyone being awarded two additional points.
xg15 11y ago
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 11y ago
  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 11y ago
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 11y ago
  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 11y ago
    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.
overpaidgoogler 11y ago
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
MatthewWilkes 11y ago
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.
paulsutter 11y ago
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 11y ago
  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.
- pitt1980 11y ago
  I'm actually not convinced that making it a higher percentage threshold doesn't make cooperation less likely at 10% (depending on class size) each student realizes that their noncooperation goes a good distance of the way towards that 10% at say 50% threshold, each student thinks their noncooperation matters less, and thus is even less likely to cooperate at least that's what I'd hypothesize, I suspect there is an interesting paper somewhere that explores this very phenomenon
- pimlock 11y ago
  He mentioned here: https://twitter.com/SelterMosby/status/619250594071638016 https://twitter.com/SelterMosby/status/619250594071638016 that for that particular group it was 20%.
- alelefant 11y ago
  Your speculation != evidence
fcbrooklyn 11y ago
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.
- jccalhoun 11y ago
  The points only matter in comparison to your classmates if there is a curve or something and the directions say there is no curve. If there is no curve then I don't see how the notion of having an advantage comes into play.
- edwardy20 11y ago
  > 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 11y ago
    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.
jmmcd 11y ago
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.
anti-shill 11y ago
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.
bsder 11y ago
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."
Tossrock 11y ago
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 11y ago
  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.
tolmasky 11y ago
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 11y ago
  Great, except votes are anonymous.
  - tolmasky 11y ago
    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 11y ago
      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 11y ago
        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.
theburg 11y ago
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?
zwrt 11y ago
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?
tolmasky 11y ago
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.
justifier 11y ago
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
acbart 11y ago
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.
deleted 11y ago
[deleted]

66 points by nkurz 11y ago

hwita 11y ago

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.

justonepost 11y ago

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

moistgorilla 11y ago
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 11y ago
  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.

andresmanz 11y ago

> 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 11y ago
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 11y ago
  You could have an auction for the 6 point slots, with the proceeds being divided and distributed to the group.
  - dogecoinbase 11y ago
    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 11y ago
      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.
      - deleted 11y ago
        [deleted]

vm 11y ago

"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.

TimPC 11y ago

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 11y ago
The article specifically state that the grades are not curved.
cortesoft 11y ago
It says in the very first paragraph of the article: "All selections are anonymous, and the course grades are not curved."

aaronchall 11y ago

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.

Smushman 11y ago

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 11y ago
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 11y ago
  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.
nadams 11y ago
I think we are missing some context - and that is very important to show if the students could communicate/collaborate (such as a homework question) or a test question. > 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. It depends on factors such as the student's current grade. I would argue you are more likely to choose 6 if you have a lower grade. > If it were the general public at large I would estimate at least 60% would choose the more personally beneficial option. Here is an related experiment. Choose N random people, and offer 2 choices: $50 or $200 and run the same experiment. Here is an interesting question - are people less "greedy" if the prizes/points have a greater span? Such as instead of 2 points and 6 what about 2 points and 20 points. I think the experiment is interesting any way you think about it.

hcurtiss 11y ago

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.

pitt1980 11y ago

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

sosuke 11y ago

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 11y ago
Agreed, but your assumption may not be correct.
- sosuke 11y ago
  You're right I vaguely remember seeing a very wide range of top scores possible. From 25 - 200
notahacker 11y ago
To pick up on the point about positional goods, everyone failing the class actually improves the ranking of [up to] half the classmates. If the points count towards some total score and there's some kind of calculation to normalize grades across the student population, everyone failing the class might actually bump up the overall grades of some of the weaker students in that class. Conversely, in this situation nobody benefits from everyone being awarded two additional points.

xg15 11y ago

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 11y ago
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 11y ago

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 11y ago
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 11y ago
  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.

overpaidgoogler 11y ago

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

MatthewWilkes 11y ago

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.

paulsutter 11y ago

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 11y ago
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.
pitt1980 11y ago
I'm actually not convinced that making it a higher percentage threshold doesn't make cooperation less likely at 10% (depending on class size) each student realizes that their noncooperation goes a good distance of the way towards that 10% at say 50% threshold, each student thinks their noncooperation matters less, and thus is even less likely to cooperate at least that's what I'd hypothesize, I suspect there is an interesting paper somewhere that explores this very phenomenon
pimlock 11y ago
He mentioned here: https://twitter.com/SelterMosby/status/619250594071638016 https://twitter.com/SelterMosby/status/619250594071638016 that for that particular group it was 20%.
alelefant 11y ago
Your speculation != evidence

fcbrooklyn 11y ago

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.

jccalhoun 11y ago
The points only matter in comparison to your classmates if there is a curve or something and the directions say there is no curve. If there is no curve then I don't see how the notion of having an advantage comes into play.
edwardy20 11y ago
> 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 11y ago
  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.

jmmcd 11y ago

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.

anti-shill 11y ago

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.

bsder 11y ago

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."

Tossrock 11y ago

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 11y ago
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.

tolmasky 11y ago

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 11y ago
Great, except votes are anonymous.
- tolmasky 11y ago
  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 11y ago
    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 11y ago
      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.

theburg 11y ago

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?

zwrt 11y ago

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?

tolmasky 11y ago

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.

justifier 11y ago

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

acbart 11y ago

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.

deleted 11y ago

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