7 ms·

>By trading places, students could get another shot at a place. At schools for which they already had a go in the lottery. This would give them better chances.

• Sniffnoy 9y ago
  > This is culturally alien to me; the students receiving the benefit are not harming other students. It's not just "culturally alien"; it's a straight-up error. > Solution: only allow trades that are in accord with the students' submitted preferences. That is, if Alice prefers Central to Devonshire, and Bob prefers Devonshire to Central, then we could allow Alice and Bob to switch if their submitted rankings indicated that these moves were consistent with their desires. There would be no incentive to lie. It's not obvious to me that this is true? Relevant discussion over on /r/math: https://www.reddit.com/r/math/comments/6uyfle/why_a_dutch_court_stopped_high_school_students/dlwtroo/ https://www.reddit.com/r/math/comments/6uyfle/why_a_dutch_co...
  • s17n 9y ago
    >> Solution: only allow trades that are in accord with the students' submitted preferences. That is, if Alice prefers Central to Devonshire, and Bob prefers Devonshire to Central, then we could allow Alice and Bob to switch if their submitted rankings indicated that these moves were consistent with their desires. There would be no incentive to lie. >It's not obvious to me that this is true? Even if you could solve the game theory issues, you wouldn't solve the problem of people selling spots in desirable schools.
  • cortesoft 9y ago
    Wait, why is that a 'straight-up error'? They explained why it would harm other students - because it would incentivize students to choose popular schools instead of schools they actually wanted, in hopes of gaining a good trade opportunity. They don't want strategy to come into play, because some people are better at strategy than others. It isn't an 'error', it is just a decision that they don't want strategy to be a factor.
    • Sniffnoy 9y ago
      Yes, the incentives this sets up could be bad for subsequent rounds; that is absolutely a real problem. But this passage seemed to be suggesting that trading, in and of itself, harmed students who were not involved in the trade, and that's not correct.
      • cortesoft 9y ago
        Something being unfair is not the same as something harming someone else. Lets say I have a cookie, and there are 10 kids in front of me who like cookies. If I give any kid a cookie for any reason, it doesn't HARM the kids who don't get a cookie; they are no better or worse off than if the cookie never existed. However, suppose I decide to give the cookie to the tallest kid - even though none of the other kids are harmed, this is still not a 'fair' situation. You can do no harm and still be unfair. Whether that is bad or not is subjective, but it is still unfair (in the sense that every kid has an equal chance at the cookie).
        • Sniffnoy 9y ago
          Sorry, I just realized that I failed to point out which part I was saying was "a straight-up error"; it's kind of buried in the sentence. My mistake! With emphasis this time: >By trading places, students could get another shot at a place. At schools for which they already had a go in the lottery. This would give them better chances. At the expense of students that don’t (or can’t) trade. This is unfair. The emphasized part is what I'm objecting to. Sorry about that.
  • LolWolf 9y ago
    This would be a stable matching (after allowing these changes). Since Nash is guaranteed here, there would be no reason to lie on the original form, unless there's some weird mixed equilibrium (that's not pure). It'd be interesting to see what conditions we must have on it (if it even exists! I'm not sure to be honest), but the only pure equilibrium is certainly a stable matching.
  • lsiebert 9y ago
    I'm curious if you could make trades automatic if all students involved benefited as per their preferences in such a way that it would be impossible to game. I think though that it would still be possible to game for any variant I can think up.
  • deleted 9y ago
    [deleted]
  • norswap 9y ago
    There's a word for that kind of error: the situation is not pareto-optimal. https://en.wikipedia.org/wiki/Pareto_efficiency https://en.wikipedia.org/wiki/Pareto_efficiency
    • ucaetano 9y ago
      > the situation is not pareto-optimal. Only in the short run it isn't. On the long run, school trading creates incentives which make the entire system worse. So you're not just optimizing for a single round of students, you're optimizing for the future rounds of students. And pareto-optimal makes no sense when you're looking at future rounds with different students. But you could create a pareto-optimal analogy: allowing two students now to trade place in a seemingly pareto-optimal way would actually harm other students when you look at the future rounds, so the trade actually isn't pareto-optimal. So it isn't an error, it's working as intended.
      • om2 9y ago
        I think he's saying that the error is in the original assignment algorithm: it produces a solution that is not Parto-optimal. If it was, there would be no mutually advantageous trades. One way it could achieve that is by randomly doing mutually improving trades until none are left.
        • ucaetano 9y ago
          But you can't consider just the current round of students when designing such a system, you need to consider all subsequent rounds. In that case, allowing trades now leads to dissatisfaction in the future. So, while allowing trades now might seem to lead to a pareto-optimal scenario, it doesn't lead to a time-series-pareto-optimal scenario.
          • om2 9y ago
            The alternate system I described doesn't involve "allowing trades" and therefore can't create perverse incentives or affect subsequent rounds. The idea is to make an algorithm that performs a Pareto-optimal assignment algorithmically, so that no possible mutually advantageous trades exist when it is done. It's totally possible for an algorithm to do that, and the current Dutch one clearly doesn't. One possible way is to run the current algorithm, and then as long as the solution is not Pareto-optimal, perform a swap at random from the set of all pairs of students where swapping would improve both of their preferences. This can be proven to converge with sufficient steps. Doing this kind of swap algorithmically has nothing to do with "allowing trades". I'm calling them "swaps" instead of "trades" here to make clear there is no manual action involved on the part of the students. I hope this clarifies what I meant, and why objecting to "allowing trades" does not make sense as a response.
  • y7 9y ago
    Suppose two students have identical rankings and end up with the same school. If one of them manages to trade (e.g. because they quickly manage to find someone that wants to trade with them), they have an advantage over the other student who is stuck with their lottery result. This is the unfairness the article talks about (besides the strategizing argument). Perhaps this can be remedied by automatic trading and another lottery, determining the order in which people get to trade, but that still doesn't solve the problem with strategic choices.
  • jpfed 9y ago
    I no longer think it's true. https://news.ycombinator.com/item?id=15069370 https://news.ycombinator.com/item?id=15069370
  • mcherm 9y ago
    > > This is culturally alien to me; the students receiving the benefit are not harming other students. > It's not just "culturally alien"; it's a straight-up error. Perhaps an exaggerated example will illustrate. Students are assigned by a lottery system that sometimes allows pairs (or triplets, etc) of students to have a beneficial trade. Then students are permitted to use dutch-school-trading.com to swap schools. Except that students who own computers are permitted to engage in this extra round of trading while students who do not own computers are not. Some consider this to be biased against students who don't own a computer. In reality, it's not the single factor of "owns a computer" which is at play, but multiple issues including social connectedness, strategic thinking, free time on the day the placements are published, and so forth.
• bjl 9y ago
  > Solution: only allow trades that are in accord with the students' submitted preferences. That is, if Alice prefers Central to Devonshire, and Bob prefers Devonshire to Central, then we could allow Alice and Bob to switch if their submitted rankings indicated that these moves were consistent with their desires. There would be no incentive to lie. This is just false. You're still incentivized to place popular schools farther up than you otherwise would.
  • jpfed 9y ago
    So what you're saying is something like... Say you have some true preferences: Heaventy Nirvana Populonopolous Shitsville Say you decide to list Populonopolous higher than Nirvana, even though you would ultimately like Nirvana better. There isn't space at Heaventy, so you are initially assigned to Populonopolous. This won't help you get into Nirvana, because you can't trade downward on your preference list. But as long as someone else got assigned to Heaventy that would have preferred Populonopolous, you could trade with them.
• oconnor663 9y ago
  > This is culturally alien to me; the students receiving the benefit are not harming other students. I think there was some similar reasoning in a Florida school vouchers case. (Which might've more recently been overturned?) Opponents of the vouchers program argued that the Florida constitution required education to be "uniform": http://www.nytimes.com/2000/03/15/us/school-vouchers-are-ruled-unconstitutional-in-florida.html http://www.nytimes.com/2000/03/15/us/school-vouchers-are-rul...
  • Spooky23 9y ago
    Vouchers are a means to get public dollars supporting parochial schools. The results are very predictable -- you can look at what happens when religious adherents take over school districts. The public schools die.
    • true_religion 9y ago
      What if 'vouchers' were implemented as a tax rebate?
      • Spooky23 9y ago
        Now instead of drawing funds directly from the district, you're subsidizing private schools at the state level. I send my son to catholic school for various reasons. It's my choice and my cost, and the school provides scholarships to help those less able. In my state, only a few things common to all students are provided/funded by the state in private schools: non-religious textbooks, school nurses, some transportation and limited bussing to special education. Personally, I'm comfortable with that model. I am uncomfortable with the state supporting any church, including my own.
        • dismantlethesun 9y ago
          > Now instead of drawing funds directly from the district, you're subsidizing private schools at the state level. In California for instance, 57% of school funding comes directly from the state, so that's no change in funding source. Personally, I don't see a difference between funding a religious school and a secular private school, both are capable of following a particular philosophical bent and applying it liberally or dogmatically. To be honest, I think the idea that we can fund any philosophy except one that touches on cosmology (i.e. religion) is an unnatural discrimination against religion.
• deleted 9y ago
  [deleted]
• abalone 9y ago
  This is exactly how it's supposed to work according to the academic whose work it is supposedly based on (Roth et al).[1] I don't know why Amsterdam didn't include automatic, mutually-advantageous trading in the algorithm. [1] http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb.17.2010.pdf http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb....
• simion314 9y ago
  Imagine school A is popular with rich kids, now I prefer not to go to A because some reasons, but I could put A on my list and if I get A then I could trade with a rich kid(and ask for some extra without authorities to know)
• ordu 9y ago
  > This is culturally alien to me; the students receiving the benefit are not harming other students. I don't think that this is culture. I believe that this is just math. If we devise some system that solves some optimization problem, we shouldn't meddle with that system by other means, like "common sense". We can use common sense to find possible improvements to the system, but we shouldn't apply this improvements without checking them with science laying behind system. Unchecked common sense can break system's promises entirely. > Solution: only allow trades that are in accord with the students' submitted preferences. That is, if Alice prefers Central to Devonshire, and Bob prefers Devonshire to Central, then we could allow Alice and Bob to switch if their submitted rankings indicated that these moves were consistent with their desires. There would be no incentive to lie. How could we know their desires? If Alice and Bob start to think creatively about it and find a way to lie about desires? Maybe they find some tradeoffs, like less chance to get into their top school against more chance to be able to trade then? The more complex system is, the more loopholes in it, the more complex and obscure strategies becomes available.
• abalone 9y ago
  > if Alice prefers Central to Devonshire, and Bob prefers Devonshire to Central, then we could allow Alice and Bob to switch... There would be no incentive to lie. To be fair, there is an incentive to lie when you add neighborhood and other preferences to the system. Say Sally, who wants Central, lives near Devonshire and thus is given better odds of getting a spot there. If Dick wants Devonshire but doesn't really care about Central, it gives him incentive to lie and rank Central higher to increase his chances of swapping with Alice. Far from an exotic scenario, this is exactly what happens in the SFUSD system.
  • abalone 9y ago
    (Edit: I meant to say Alice, not "Sally". No idea why my mind substituted that name.)