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Suspicious Discontinuities (2020)

danluu.com

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Re: Suspicious Discontinuities (2020)

#41

Post by aesthesia »

jameshart wrote: post #26
irishcoffee wrote: post #10

Earlier quoted context omitted.

The reddit explanation in the post addresses your question I believe. If someone is at a 28 or 29 a few "charity" points can be found in subjectively-graded tests.

I think that really just reflects the fact that on subjectively graded tests the score really doesn’t have that many significant figures of accuracy. That a regrading can find 3 to 5 points by being more generous - or presumably take 3 to 5 off by being harsher - says that really you could save a lot of effort by treating the final grades as bucketing into 10 point bands and treating 25-35 as the actual cutoff.

Isn't that equivalent to just setting the passing threshold to 25, with the same incentives?

Re: Suspicious Discontinuities (2020)

#42

Post by bee_rider »

tmoertel wrote: post #31
hsuduebc2 wrote: post #5

I never understood why taxes or similiar absolute points aren't gradients instead.

Why do we have legislated cliffs instead of gradients? Because approximately nobody understands lerp. And linear interpolation is the simplest (nontrivial) gradient scheme. Consequently, we get cliffs or, if we're lucky, lookup tables that approximate gradients with stair-step successions of small cliffs.

This isn’t a very satisfying explanation to me. I mean, the idea of a cliff causing bad incentives is extremely widely understood (to the point where people under progressive taxation policies avoid taking overtime because they misunderstand the policy and believe the cliff to be there).

I wonder why we don’t define these things in terms of logistic functions or something. That’s high school or at least first semester college math, right?

Re: Suspicious Discontinuities (2020)

#43

Post by dadkins »

Jim Roskind had a really nice talk [https://www.youtube.com/watch?v=_uaaCiyJCFA] at AWS Reinvent 2022 which highlighted the fence post problem. Basically, AWS was targeting P50 and P90 latencies in many services, and sure enough there were big clumps of latencies right under those target fence posts as engineers were basically gaming the metrics and nerfing the >P90 latencies to make it happen.

Re: Suspicious Discontinuities (2020)

#44

Post by ant6n »

Haven’t seen danluu stuff here for a while!

One way to reduce income may be to buy a bunch of stocks with high variance - for any that is in the red during the year, sell and rebuy them. Any that has a gain, leave them be.

Re: Suspicious Discontinuities (2020)

#45

Post by [deleted] »

fwipsy wrote: post #4

I cracked up when I got to the marathon example. When I ran a half marathon I realized about 80% of the way through that I was on track to finish under 2:30:00 and pushed myself to make it happen. I should have guessed that sort of behavior would show up in the statistics!

[deleted]

Re: Suspicious Discontinuities (2020)

#46

Post by zipy124 »

bostik wrote: post #13
blharr wrote: post #12

Earlier quoted context omitted.

I think because the gradient is simply too confusing for laypeople to understand. Even for a simple system like US social security that has a gradient. For every $2 you make over the limit, you lose $1 in benefits. I've heard countless times misconceptions of people thinking they'd be losing money (as in literally having less money net) by working.

This does happen in Finnish tax system. Your tax rate (percent with one decimal) is calculated based on your annual gross income. Rates are supposed to be calculated smoothly, and they are certainly calculated for each individual separately. In reality they are step functions. It is surprisingly common to have people refuse promotions because if would put them above an income tax threshold, bump up their rate, and en…

The UK system doesn't either though. The rate for 100-125k is higher than for 125k+ due to the phasing out of the personal allowance. It gets worse if you have kids and can even result in a >100% marginal rate.

Re: Suspicious Discontinuities (2020)

#47

Post by brightbeige »

chantepierre wrote: post #11
fwipsy wrote: post #4

I cracked up when I got to the marathon example. When I ran a half marathon I realized about 80% of the way through that I was on track to finish under 2:30:00 and pushed myself to make it happen. I should have guessed that sort of behavior would show up in the statistics!

After this year's Paris marathon, I ran the same per-minute graphs, and they match perfectly the "overall study" graphs with more than 9 million finishes in the article. I also added graphing by age category and gender. I don't want to deduce too much but I think it showed that young men are the most "competitive" (what I mean by that is targeting a specific time) since there are the clearest "goal time" peaks in the…

IIRC There is also a discontinuity when it comes to the histogram of ages of marathon runners, because runners are binned into age groups and there is a more runners at the youngest ages of each group, I guess because it’s younger runners in each group that are more likely to run if they feel more likely to place well in their group

Re: Suspicious Discontinuities (2020)

#48

Post by [deleted] »

forbiddenlake wrote: post #23
PaulDavisThe1st wrote: post #8

[ EDIT: Since the undated article is actually from Feb 2020, predating the expansion of federal health insurance subsidies, I withdraw everything I said below. ] ---------------------------------- The opening story is fabricated and/or bullshit. Last year (2025) there was no limit on income for health insurance subsidies. That ended for this year, but last year there would have been no reason for anyone who knew what…

The post is from February 2020. I can't see a date on the post (on mobile) but the archives link has month and year.

[deleted]

Re: Suspicious Discontinuities (2020)

#49

Post by bobbiechen »

ant6n wrote: post #44

Haven’t seen danluu stuff here for a while! One way to reduce income may be to buy a bunch of stocks with high variance - for any that is in the red during the year, sell and rebuy them. Any that has a gain, leave them be.

The wash sale rule (in the US) makes it a lot harder to pull this off.

Re: Suspicious Discontinuities (2020)

#50

Post by benjiro29 »

ajsnigrutin wrote: post #22
mnahkies wrote: post #3

The UK tax system also has a bunch of unfortunate cliffs, and tapers that create >60% marginal tax rates and worse. There's a calculator here that illustrates it well https://tax-cliffs.britishprogress.org/calculator The childcare cliff edge is probably the worst, but the personal allowance taper isn't ideal either as it's compressed over a relatively short income range And of course all the thresholds remain frozen,…

Same in slovenia for eg. kindergarten prices, 1eur over the line, 90eur more per month in fees.

I remember when my grandfather died, and my grandmother got part of his pension.

It put her pension above a max threshold for old age / low pension (cheaper phone bill, no tv taxes, ...) by, ... hold your hats... 2 Euro.

Father called the service ... "sorry, we can not do anything about that".

She lost over 100 Euro in benefits because technically... she was not low pension anymore but was financially WAY more poor then when my grandfather was alive.

So when my grandfather was alive, their combined pension was higher, they qualitied as having a low pension. When only *part* of my grandfather pension got combined into my grandmothers. Well, now your not poor...

I do not remember the exact pensions but it was a massive haircut, with the insulting on top, losing those benefits. The lost benefits made it from threading water, to drowning.

Without my dad financial help, she will have lost the house. Ironically, if she did not get my grandfathers pension part, she will have qualitied for more social assistance, and will have been better off.

Sometimes, those lines really screw people over.

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