Silence

This post from Worthwhile Canadian Initiative is probably the best reason for my recent lack of activity in the blogosphere. Coupled with a lot of travel, I am quite behind.

Hopefully a temporary condition.

In the meantime, Mark has been putting up some great material that is well worth reading, so at least radio silence hasn't struck yet.

Quick note on good stuff

No time to blog this afternoon but if there was I'd join in this discussion on polls and momentum. While you're there, take a minute to check out the comments.

On 'Good Morning America': Worthy defends plan to jail parents who skip school conferences

From The Detroit News:

Wayne County Prosecutor Kym Worthy defended her plan to jail parents who repeatedly miss conferences with their children's teachers during an appearance today on ABC's "Good Morning America."

Worthy said many people think she is looking to simply jail people for three days if they miss a parent-teacher conference, but she said her plan is not that strict. She is calling for the jail stay if a parent repeatedly misses conferences and isn't in touch with teachers and school officials.

Parents of achieving students are exempt and a parent who is in constant contact with the school also is exempt. Worthy said a parent could miss three or four conferences before officials would start looking as to why they were not attending them. Those with medical conditions also would be exempt.

I'm not going to get into the appropriateness or effectiveness of this proposal, but it is another reminder how different the population of charter schools is.

I taught in an inner-city prep school targeting serving lower income students, a school run by some of the most dedicated educators I've ever encountered. They took kids who were performing below grade level (sometimes by more two grades) and got almost all of them into college.

When I say almost all, I mean almost all. The drop-out rate was extremely low. This was possible partly because the administrators made it a priority and partly because schools with admission processes tend to select out many of the most at-risk students. (This is why we expect charter schools to have lower drop-out rates than comparable public schools, and why we are so concerned when we see the opposite.)

But as dedicated and hard working as the faculty and administration of that school was, every one of them would tell you that the engaged and supportive families of the kids made their jobs much, much easier. When there was a parents' night you could expect pretty much one hundred percent attendance and when there was a problem with a student you could pretty much count on a concerned response.

Public school teachers and administrators seldom have those advantages.

And yes, it does make a difference.

More fun and games

I've got a new post up at Education and Statistics on the topological doodling game, Sprouts. If topological doodling strikes you as an enjoyable way to spend your time, I highly recommend that you check this out.

Tax increases as landscape perturbation?

Over at Felix Salmon's site, Justin Fox presents an interesting counter-argument to Greg Mankiw:

[T]here’s a really fascinating tale in [Sam Howe Verhovek’s Jet Age: The Comet, the 707, and the Race to Shrink the World] involving tax incentives. During the Korean War, Congress enacted an excess profits tax meant to keep military contractors from, well, profiteering. In its infinite wisdom, Congress defined excess profits as anything above what a company had been making during the peacetime years 1946-1949.

Boeing was mostly a military contractor in those days (Lockheed and Douglas dominated the passenger-plane business), and had made hardly any money at all from 1946 to 1949. So pretty much any profits it earned during the Korean conflict were by definition excess, and its effective tax rate in 1951 was going to be 82%. This was unfair and anti-business. If similar legislation were enacted today, you could expect U.S. Chamber of Commerce members to march on Washington and overturn cars on the streets.

It being 1951, Boeing instead sucked it up and let the tax incentives inadvertently devised by Congress steer it toward a bold and fateful decision. CEO Bill Allen decided, and was able to persuade Boeing’s board, to plow all those profits and more into developing what became the 707, a company-defining and world-changing innovation. Writes Verhovek:

Yes, it was a huge gamble, but for every dollar of the dice roll, only eighteen cents of it would have been Boeing’s to keep anyway. For Douglas and Lockheed, both in a much lower tax bracket, that was not so easy a call.

So that’s it! High tax rates—confiscatory tax rates—spur innovation! Well, at least once in a blue moon they do. Which is an indication that there might be some important stuff missing from the classic economists’ view of taxation, as summed up by Greg Mankiw a few weeks ago:

Economists understand that, absent externalities, the undistorted situation reflects an optimal allocation of resources. It is crucial to know how far we are from that optimum. To be somewhat nerdy about it, the deadweight loss of a tax rises with the square of the tax rate.

Somehow I don’t think that formula held true in Boeing’s case.

This leads me to wonder if this reminds anyone else of algorithms that locate superior optima by slightly perturbing fitness landscapes (processes closely related to simulated annealing). Mankiw complains that certain taxes distort the economic landscape, but if local optimization is an issue (as was apparently the case with Boeing), then mild distortion from time to time is likely to lead to a better performing economy.

For background, here's an excerpt from a post on landscapes. The subject was lab animals but the general principles remain the same:

And there you have the two great curses of the gradient searcher, numerous small local optima and long, circuitous paths. This particular combination -- multiple maxima and a single minimum associated with indirect search paths -- is typical of fluvial geomorphology and isn't something you'd generally expect to see in other areas, but the general problems of local optima and slow convergence show up all the time.

There are, fortunately, a few things we can do that might make the situation better (not what you'd call realistic things but we aren't exactly going for verisimilitude here). We could tilt the landscape a little or slightly bend or stretch or twist it, maybe add some ridges to some patches to give it that stylish corduroy look. (in other words, we could perturb the landscape.)

Hopefully, these changes shouldn't have much effect on the size and position of the of the major optima,* but they could have a big effect on the search behavior, changing the likelihood of ending up on a particular optima and the average time to optimize. That's the reason we perturb landscapes; we're hoping for something that will give us a better optima in a reasonable time. Of course, we have no way of knowing if our bending and twisting will make things better (it could just as easily make them worse), but if we do get good results from our search of the new landscape, we should get similar results from the corresponding point on the old landscape.


* I showed this post to an engineer who strongly suggested I add two caveats here. First, we are working under the assumption that the major optima are large relative to the changes produced by the perturbation. Second our interest in each optima is based on its size, not whether it is global. Going back to our original example, let's say that the largest peak on our original landscape was 1,005 feet tall and the second largest was 1,000 feet even but after perturbation their heights were reversed. If we were interested in finding the global max, this would be be a big deal, but to us the difference between the two landscapes is trivial.

Nothing like a good graph to convey bad news

There's an extensive and erudite discussion of this over at Economist's View, with voices ranging from Krugman to Mankiw.

Nate Silver tries to disabuse political reporters of another favorite myth

In today's 538, Nate Silver takes down the myth that polls tend to show momentum. He left out some details that OE readers might be curious about (but, of course, we're not exactly the target audience), but it's an excellent piece of statistical writing.

The Misunderstanding of Momentum

By NATE SILVER

Turn on the news or read through much of the analysis put out by some of our friends, and you’re likely to hear a lot of talk about “momentum”: the term is used about 60 times per day by major media outlets in conjunction with articles about polling.

When people say a particular candidate has momentum, what they are implying is that present trends are likely to perpetuate themselves into the future. Say, for instance, that a candidate trailed by 10 points in a poll three weeks ago — and now a new poll comes out showing the candidate down by just 5 points. It will frequently be said that this candidate “has the momentum”, “is gaining ground,” “is closing his deficit,” or something similar.

Each of these phrases are in the present tense. They create the impression that — if the candidate has gone from being 10 points down to 5 points down, then by next week, he’ll have closed his deficit further: perhaps he’ll even be ahead!

There’s just one problem with this. It has no particular tendency toward being true.

Read the rest...

A probabilistic mystery from Alfred Hitchcock

Don't believe me? See for yourself.

Yet another trillionaire protesting the return to Clinton era taxes

And this guy's practically swimming in money.

Lucky pennies and constrained roulette

In a recent post about progressive taxation, Jonathan Cohn says the following about economic fairness:

One is that it fails to account for the power of luck. Almost by definition, people who are successful have benefited from some measure of good fortune. That fortune can take the form of obvious, material advantages -- like access to advanced technology and good schools. Or it can take the form of more subtle, but still important, assets for moving forward in life--like good health or loving parents.

There's no arguing with the basic thrust here, but it presents a very narrow view of luck. You can get a broader and more interesting view if you think in terms of probability distributions.

The idea of luck is closely tied to the idea of beating the odds. Having an unlikely positive outcome is more or less equivalent to the informal concept of being 'lucky,' but this often leads into one of those areas of probability that give people trouble.

There's a natural and entirely rational impulse to look for explanations when we see something unlikely. Unfortunately, there's also a natural tendency to get confused when we go back and assign probabilities after the fact.

One of the best known examples comes from Burton Gordon Malkiel in his classic A Random Walk Down Wall Street. Malkiel draws an analogy between a successful investment fund manager and a lucky coin-flipper.

Imagine a coin flipping competition. You start with a thousand coin-flippers. Every round consists of one flip. At the end of every round, those who came up tails leave the game. The contestants go from 1,000 to 500 to 250 to 125 to 63 to 31 to 16 to 8.

"By this time, crowds start to gather to witness the surprising ability of these expert coin-flippers. The winners are overwhelmed with adulation. They are celebrated as geniuses in the art of coin-flipping, their biographies are written and people urgently seek their advice. After all, there were 1,000 contestants and only 8 could consistently flip heads."

As presented here, this seems absurd but if you spend some time watching CNBC or browsing the business section of your local book store, you'll realize it's not exaggerated.

Related to the lucky coin-flipper is the grand prize winner.

We have a roulette wheel numbered 1 to 100, 100 spaces on the table and 100 players. On a first come, first serve basis, each player picks a number. Whoever is sitting on the number that comes up gets everyone's chips.

The winner can argue that he or she had some special skill at number picking, and that's entirely possible, but there's no way of confirming that claim by looking at the results of the game. Someone had to win and whoever won could make the same argument.

Just as it's not difficult to find lucky coin flippers, it's also easy to find CEOs and business leaders who benefited greatly from landing on the right number.

Consider Michael Eisner.

Eisner was CEO of Disney from 1984 to 2005. By any standard it was a good run, marked by growth, major acquisitions, prestigious and popular products. Eisner deserves credit for a lot of good decisions, but the single biggest factor behind Disney's resurgence came from a turn of the roulette wheel.

In the late Eighties, with the format war settled and VCR reaching saturation levels, parents discovered that the easiest (and often the only) way to keep a small child quiet was to pop in a video (I recall Robert Altman saying in an interview that Popeye was his most profitable film for just this reason). Suddenly Disney was sitting on the most valuable film library in the world.

It is true that Eisner pushed to speed up release of some of the studio's classics, but the home video division had started years before he got there and given the size of the market that opened up, it's hard to believe that even the most cautious of executives would have held back the films much longer.

Michael Eisner simply found himself sitting on a lucky number.

If a sock puppet had been appointed CEO of Disney in 1984, the home video market for kid-friendly shows would still have exploded and the company still would have made a mint. It might not have managed a Little Mermaid or a Lion King but it still would have had a fantastic run and you'd have no trouble finding numerous books exploring the business genius of Argus McArgyleSock.

In praise of orifice-derived numbers

HCZ founder Geoffrey Canada in an interview with City Limits Magazine:

You have set a 65 percent "tipping point" as a universal goal for your programs, after which you think success becomes inevitable. How did you determine that 65 percent was the tipping point?

Why that number? Why that number and not 70, 80 percent? There's no science there. You don't go look up, find the tipping point of a poor community—there's no science there. You take your best educated guess...

I'll tell you what my belief is, and what's my underlying logic. Kids do what their friends do. If your friends smoke, you smoke. If your friends drink, you drink. That's just the way things are. Kids do what they're around. If you're around kids who fight, you better learn how to fight. If you get a whole bunch of kids doing positive things instead of negative things, should you expect that to have an impact on other kids? Absolutely. But there's no science.

If the question is, is there science, has someone done a randomly controlled double-blind study? No, no. But ask anybody. You want the Harlem Children's Zone on your block, working with the kids on your corner, or not? You don't need a random study to decide what the answer to that is. You ask people, when a shooting happens, do you want folks from the Harlem Children's Zone to go in there and make sure no one else gets shot or not? You live in Harlem, guess who you're calling? You're calling me.

I liked this answer.

As a statistician, I am frequently asked quantify difficult-to-measure variables and estimate parameters for decision processes. In these situations I can always find some rational-sounding process for deriving a metric, but I can't always vouch for its robustness or even its relevance and there's a good chance all it will do is give the recipient a false sense of security. Some things just don't readily lend themselves to these approaches.

People like the notion of processes being data-driven. They feel safer knowing that there methodologies and statistics behind the decisions that affect them. Unfortunately a suspect methodology and a statistic that doesn't measure what it's meant to can do tremendous damage. If I'm ask to produce metrics when I don't have faith in the analyses or in our ability to measure what's relevant, then as a statistician, the best and most responsible answer I can give is often, "Hell, I don't know. What sounds reasonable to you?"*

There's a lot to be said for an arbitrary number that's reasonable to the people who actually work in the field, particularly if that number is also a good and useful rule of thumb. Of course, it could turn out to be a poor estimate of what you're after but the same holds for the results of bad data and analyses and it's a great deal easier to drop a number when it doesn't come with pages of impressive-looking but meaningless tables.






* I'm not going to wander off into a discussion of informative priors here, but these woods are filled with Bayesians so there's a good chance someone will pick up the scent.

LA Weekly doesn't just bury the lede; they hide the body

(It's Sunday so I'm taking a break from bitching about bad statistics so I can bitch about bad journalism.)

LA Weekly's Jonathan Gold is the first food writer to win a Pulitzer and for a first, it was a remarkably uncontroversial award. Gold has been widely recognized for his sharp, funny prose and his knowledgeable and discerning approach to criticism.

(That has nothing to do with the topic of the post but I wanted to start with something nice.)

With the exception of Gold, the Weekly offers pretty much the standard free-weekly fare, specializing in starkly-lit heroes-and-villains stories with obligatory swipes at the mainstream media (particularly peevish and resentful when focusing on their competition).

One of the problems with writing this sort of story is that, if you're going to stay true to the narrative you invariably have to leave out something funny and/or interesting because it undercuts your case.

For example, if you were writing a story about a sleazy conman slandering respectable businesses, you wouldn't be able to include a quote that made one of those respectable businesses look completely street-rat crazy. That's too bad, because it must be difficult to ask a journalist to pass up anything as memorable as this (from Felix Salmon, who almost never leaves out the good stuff):

On Monday, Barry Minkow put out a press release accusing a NYSE-listed company, InterOil, of being “nothing more than hype”. InterOil has had a large short interest for some time, and it seems that Minkow touched a nerve, because InterOil’s senior manager for media relations, Susuve Laumaea, went borderline insane via email in response:

you are a gutless coward of the highest order, a jealous and envious SOB… You are a loser, a non-achiever and a sour-grape. Piss off you good for nothing… Do not be afraid on account of me being a descendant of cannibals … no, no, believe me, I will not cannibalise you or feed you to the swamp crocodiles…

you are known crook, conman, convicted felon, a psychopath and a pathological liar who is jealously envious… You have no sense of common decency. You are neither here nor there among the cream of decent God- fearing humanity. You are a scum of the earth, a creepy-crawlie who should have been locked away and the key thrown away too so that you rot away like the dung heap you are. You are a coward of the highest order… I can’t use you as crocodile feed because you are too poisonous … those alligators will die eating you, cooked or uncooked…

Who gave you the authority to investigate InterOil, you piece of shitty non-entity? You are nothing more than an internet pirate, a low-life manipulator who is out to profit by your dishonest, fraudulent, slanderous and cowardly methods. Up yours.

How could the Weekly leave this out? It's like Beat poetry. It practically demands to be read aloud with dramatic pauses and bongo accompaniment.

Benoît Mandelbrot (1924 - 2010) and Education Reform

From A maverick's apprenticeship:

It was then and there that a gift was revealed. During high school and the wandering year and a half that followed, I became intimately familiar with a myriad of geometric shapes that I could instantly identify when even a hint of their presence occurred in a problem. “Le Père Coissard,” our marvelous mathematics professor, would read a list of questions in algebra and analytic geometry. I was not only listening to him but also to another voice. Having made a drawing, I nearly always felt that it missed something, was aesthetically incomplete. For example, it would improve by some projection or inversion with respect to some circle. After a few transformations of this sort, almost every shape became more harmonious. The Ancient Greeks would have called the new shape “symmetric” and in due time symmetry was to become central to my work. Completing this playful activity made impossibly difficult problems become obvious by inspection. The needed algebra could always be filled in later. I could also evaluate complicated integrals by relating them to familiar shapes.

I was cheating but my strange performance never broke any written rule. Everyone else was training towards speed and accuracy in algebra and reduction of complicated integrals; I managed to be examined on the basis of speed and good taste in translating algebra back into geometry and then thinking in terms of geometrical shapes.

Where did my gift come from? One cannot unscramble nature from nurture but there are clues. My uncle lived a double life as weekday mathematician and Sunday painter. My gift for shapes might have been destroyed, were it not for the unplanned complication of my life during childhood and the War. Becoming more fluent at manipulating formulas might have harmed this gift. And the absence of regular schooling influenced many life choices, but ended up not as a handicap but as a boon.

I realize we can't have an educational system focused entirely on the occasional Mandelbrot, but I can't help but wonder how the great man would have fared in the rigid, metric-driven system we're headed toward.

(also posted at Education and Statistics)

"No, I said 'self-select for attitude.'"

One of the many weird aspects of the charter school debate has been the non-exchanges over selection effects. Critics suggest that students who choose to go through the application process will tend to be more motivated, more committed to school, more interested in college, and more open to the idea of a heavier work load and will tend to have more stable, supportive families.

Here's an example:

Some observers, such as the authors of The Charter School Dust-Up, say that KIPP's admission process self-screens for students who are both motivated and compliant, from similarly motivated and compliant—and supportive—families. Parents must commit to a required level of involvement, which rules out badly dysfunctional families.

This would seem to be fairly straightforward. Almost every school could do a good job if it were populated solely by students who worked hard, followed instructions and had the full support of their families. A strong selection effect here could explain away most or all of the positive results observed in KIPP schools. This hypothesis even raises the possibility that KIPP schools are actually doing worse than public schools would under comparable circumstances.

(You'll notice that no mention is made of race, poverty or test scores.)

Now here's how SRI responds:

KIPP schools’ higher-than-expected test score results draw both attention and claims that they “cherry-pick” high-achieving students from poor neighborhoods. This is the first report to closely scrutinize the praise and criticisms associated with KIPP, as well as key challenges facing Bay Area KIPP schools today.

In the three KIPP schools where they were able to draw comparisons, SRI researchers found that students with lower prior achievement on the CST were more likely to choose KIPP than higher-performing students from the same neighborhood, suggesting that, at least at these schools, cherry-picking does not occur.

And here's the much-touted Mathematica report:

Our nonexperimental methods account for the pre-KIPP (baseline) characteristics of students who subsequently enter KIPP schools: not only demographic characteristics such as race/ethnicity, gender, poverty status, and special education status, but also their achievement test results for two years prior to entering KIPP. We examine the achievement levels of the students for up to four years after entering KIPP schools. In our preferred models, we compare these trajectories to the achievement trajectories of a matched set of local public school students who have similar achievement test results and demographic characteristics in the baseline period (typically third and fourth grades) but who do not enroll in KIPP.

Waiting for Superman... to get bored and drop you like a bad habit

From Roger Ebert's review of Waiting for Superman:

We have met five of these students, heard from them and their parents, and hope they'll win. The cameras hold on their faces as numbers are drawn or names are called. The odds against them are 20 to 1. Lucky students leap in joy. The other 19 of the 20 will return to their neighborhood schools, which more or less guarantees they will be part of a 50 percent dropout rate. The key thing to keep in mind is that underprivileged, inner-city kids at magnet schools such as Kipp L.A. Prep or the Harlem Success Academy will do better academically than well-off suburban kids with fancy high school campuses, athletic programs, swimming pools, closed-circuit TV and lush landscaping. [emphasis added]

Probably the most comprehensive study of the KIPP program was done by SRI, which looked at KIPP schools in the Bay Area. Here's one of their findings (again, emphasis added):

As researchers analyzed the student achievement data and KIPP’s approach, they also identified challenges facing Bay Area KIPP schools, including high student attrition rates, teacher turnover, and low state and local funding. For example, 60 percent of students who entered fifth grade at four Bay Area KIPP schools in 2003-04 left before completing eighth grade.

More that any other player in the charter school movement, KIPP has relied on the cheese effect to generate its results. It's a profitable and highly praised business model built entirely of the backs of discarded students.