Comment by abalone | Hacker News Reader

Comment by abalone | Hacker News Reader

San Francisco United School District uses the multi-DA system, but here's the kicker: it bakes exchanging into the algorithm.[1] They call it "trading up"; most parents here refer to it as "swapping".

It works more or less as described, where you list off all the schools you want in order of preference. It runs lotteries for each of them in parallel and you get the highest listed one you win. But then it does one more thing: If it finds mutually advantageous swaps, it does so automatically and instantly. In other words, it's not up to or necessary for the student to do it manually.

In fact this feature is detailed by the Ivy League team that put it together, including Alvin Roth, as early as 2010.[2] So while this article is well written it seems to give a less than complete picture. Why did Amsterdam not adopt this feature?

P.S. There is much to be said about the SF lottery system which is a fun / highly stressful topic for nerds and parents. If you like these kinds of problems I encourage you to take a look. It also tries to solve for giving preferences to neighborhood schools and disadvantaged families, while also offering special language and K-8 programs that serve the whole city fairly. The goal is to eliminate strategizing as much as possible, but it's very interesting to see people figure out some hacks.

[1] http://www.sfusd.edu/en/assets/sfusd-staff/enroll/files/2012...

[2] http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb....

I disagree about the "fun" part having just gone through this with my first kid. I agree with the Dutch, swapping (at any point in time) adds an edge of unfairness to the process:

- In a situation where all decent schools are oversubscribed swapping 100% encourages (and rewards) setting up your school list strategically. Which helps out families that have the time to collect the information needed and sort their schools appropriately (we spent a bunch of time researching / planning here, but knew off other families who _really_ got into gaming the system)

- In one of the meetings where the slide you linked in [1] was displayed, they offhand mentioned that the swapping order is done alphabetically. When asked if kids with A* names will get better swaps they kinda ignored the question and moved on. But how are multiple tied swaps resolved?

- Also, from what we were told, the swapping doesn't respect the "lottery weight" that locals, poor test score neighborhood kids, or siblings get. If that's important, shouldn't it apply to all phases of the process? (I'm aware the math here might get out of hand)

I started out thinking that the swapping was a good idea, but when I saw how much it encouraged and rewarded strategy in building the list of schools I changed my mind. It's not a fair process. It's a system that rewards families that have likely already been rewarded by society.

> If that's important, shouldn't it apply to all phases of the process?

Doesn't that same reasoning apply to increasing the weight? Maybe it's so important and not more important.

Can you be more specific about the strategies that help with building the list of schools?

This incentivises people to put popular schools which they don't like lower on their list (3-5), so that if they miss their top school, they can get into a popular school and swap with people who are at their desired school. Which removes the property that honesty in school rankings is the best policy.

Yeah, but what if they do like the popular school as a backup? Wouldn't eliminating swaps lower the average rank of assigned schools, and thus decrease happiness?

Lower average rank of assigned schools might mean decreased happiness, but this system also increases fairness because those who game the system tend to be better educated/more privileged. Disallowing swaps forces people to rank schools honestly and prohibits such gaming of a system.

I haven't heard flattering things about SF school system--mostly directed at the lottery. I remember hearing that half of kids born in SF move away before entering school, another half go to private school. I can't find the source, but I had read this article when it was published[1]. It says 30% of students go to private schools.

[1] https://www.nytimes.com/2017/01/21/us/san-francisco-children...

That's not necessarily due to the lottery alone. That will happen when the schools are underfunded and less desirable than private, regardless of how equitably assignments are distributed.

A majority of students get their first choice public school.[1] However there is a lot of competition for a handful of the most desired schools. Only a small percentage of students request their local school first, but if you live near a popular school and you don't get it, it is frustrating. You may end up getting placed at a much less desirable school farther away. People blame the lottery for that, but ultimately the "best" schools don't have enough seats.

[1] http://www.sfusd.edu/en/assets/sfusd-staff/enroll/files/2015...

This sounds a lot like the Single Transferable Vote system that some of us are pushing for in Canada. Same principle, you rank all of the parties that are acceptable to you, and your vote is applied to the first candidate who isn't eliminated.

This way, if I want the Green party, and am willing to settle for Liberals, but can't stand the thought of a Conservative win, then I can support my favorite party without risking a split vote that lets the hated party squeak in with ~38% of the vote. Naturally, those of us who vote for fringe parties are strongly in favor of STV, and those who benefit from split votes complain that it is too complex for the average voter to understand.

You might find Mixed Member Proportional an interesting option. It is directly proportional in the party vote and also includes electorate MPs. It does not suffer from some of the strategic voting problems that STV suffers from.

Interesting, I'm liking the separation of concerns here. My favorite MLA is riding on the wrong party, but MMP would solve that conundrum nicely.

But the problem with schools is different in the sense that each candidate can only accept a finite amount of votes.

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