And for today, at least, you are not the world's biggest math nerd

From Greg Mankiw:

Fun fact of the day: MIT releases its undergraduate admission decisions at 1:59 pm today. (That is, at 3.14159).

Who is this Thomas Jefferson you keep talking about?

I've got some posts coming up on the role curriculum plays in educational reform. In the meantime, check out what's happening in Texas* with the state board of education. Since the Lone Star state is such a big market they have a history of setting textbook content for the nation.

Here's the change that really caught my eye:

Thomas Jefferson no longer included among writers influencing the nation’s intellectual origins. Jefferson, a deist who helped pioneer the legal theory of the separation of church and state, is not a model founder in the board’s judgment. Among the intellectual forerunners to be highlighted in Jefferson’s place: medieval Catholic philosopher St. Thomas Aquinas, Puritan theologian John Calvin and conservative British law scholar William Blackstone. Heavy emphasis is also to be placed on the founding fathers having been guided by strict Christian beliefs.

* I'm a Texan by birth. I'm allowed to mock.

Observational Research

An interesting critique of observational data by John Cook. I think that the author raises an interesting point but that it is more true of cross-sectional studies than longitudinal ones. If you have a baseline modifiable factor and look at the predictors of change then you have a pretty useful measure of consequence. It might be confounded or it might have issues with indication bias, but it's still a pretty interesting prediction.

With cross sectional studies, on the other hand, reverse causality is always a concern.

Of course, the other trick is that the risk factor really has to be modifiable. Drugs (my own favorite example) often are. But even diet and exercise get tricky to modify when you look at them closely (as they are linked to other characteristics of the individual and are a very drastic change in lifestyle patterns).

It's a hard area and this is is why we use experiments as our gold standard!

"The Obesity-Hunger Paradox"

Interesting article from the New York Times:

WHEN most people think of hunger in America, the images that leap to mind are of ragged toddlers in Appalachia or rail-thin children in dingy apartments reaching for empty bottles of milk.

Once, maybe.

But a recent survey found that the most severe hunger-related problems in the nation are in the South Bronx, long one of the country’s capitals of obesity. Experts say these are not parallel problems persisting in side-by-side neighborhoods, but plagues often seen in the same households, even the same person: the hungriest people in America today, statistically speaking, may well be not sickly skinny, but excessively fat.

Call it the Bronx Paradox.

“Hunger and obesity are often flip sides to the same malnutrition coin,” said Joel Berg, executive director of the New York City Coalition Against Hunger. “Hunger is certainly almost an exclusive symptom of poverty. And extra obesity is one of the symptoms of poverty.”

The Bronx has the city’s highest rate of obesity, with residents facing an estimated 85 percent higher risk of being obese than people in Manhattan, according to Andrew G. Rundle, an epidemiologist at the Mailman School of Public Health at Columbia University.

But the Bronx also faces stubborn hunger problems. According to a survey released in January by the Food Research and Action Center, an antihunger group, nearly 37 percent of residents in the 16th Congressional District, which encompasses the South Bronx, said they lacked money to buy food at some point in the past 12 months. That is more than any other Congressional district in the country and twice the national average, 18.5 percent, in the fourth quarter of 2009.

Such studies present a different way to look at hunger: not starving, but “food insecure,” as the researchers call it (the Department of Agriculture in 2006 stopped using the word “hunger” in its reports). This might mean simply being unable to afford the basics, unable to get to the grocery or unable to find fresh produce among the pizza shops, doughnut stores and fried-everything restaurants of East Fordham Road.

"The economics profession is in crisis"

This may sound strange but all this soul searching by economists like Mark Thoma makes me think that the field might be on the verge of extensive reassessment and major advances.

From the Economist's View:

The fact that the evidence always seems to confirm ideological biases doesn't give much confidence. Even among the economists that I trust to be as fair as they can be -- who simply want the truth whatever it might be (which is most of them) -- there doesn't seem to be anything resembling convergence on this issue. In my most pessimistic moments, I wonder if we will ever make progress, particularly since there seems to be a tendency for the explanation given by those who are most powerful in the profession to stick just because they said it. So long as there is some supporting evidence for their positions, evidence pointing in other directions doesn't seem to matter.

The economics profession is in crisis, more so than the leaders in the profession seem to understand (since change might upset their powerful positions, positions that allow them to control the academic discourse by, say, promoting one area of research or class of models over another, they have little incentive to see this). If, as a profession, we can't come to an evidence based consensus on what caused the single most important economic event in recent memory, then what do we have to offer beyond useless "on the one, on the many other hands" explanations that allow people to pick and choose according to their ideological leanings? We need to do better.

(forgot to block-quote this. sorry about the error)

TNR on the education debate

The New Republic is starting a series on education reform. Given the extraordinary quality of commentary we've been seeing from TNR, this is definitely a good development.

Here are the first three entries:

By Diane Ravitch: The country's love affair with standardized testing and charter schools is ruining American education.

By Ben Wildavsky: Why Diane Ravitch's populist rage against business-minded school reform doesn't make sense.

By Richard Rothstein: Ravitch’s recent ‘conversion’ is actually a return to her core values.

Harlem Children's Zero Sum Game

I used to work in the marketing side of large corporation (I don't think they'd like me to use their name so let's just say you've heard of it and leave the matter at that). We frequently discussed the dangers of adverse selection: the possibility that a marketing campaign might bring in customers we didn't want, particularly those we couldn't legally refuse. We also spent a lot of time talking about how to maximize the ratio of perceived value to real value.

On a completely unrelated note, here's an interesting article from the New York Times:

Pressed by Charters, Public Schools Try Marketing
By JENNIFER MEDINA

Rafaela Espinal held her first poolside chat last summer, offering cheese, crackers and apple cider to draw people to hear her pitch.

She keeps a handful of brochures in her purse, and also gives a few to her daughter before she leaves for school each morning. She painted signs on the windows of her Chrysler minivan, turning it into a mobile advertisement.

It is all an effort to build awareness for her product, which is not new, but is in need of an image makeover: a public school in Harlem.

As charter schools have grown around the country, both in number and in popularity, public school principals like Ms. Espinal are being forced to compete for bodies or risk having their schools closed. So among their many challenges, some of these principals, who had never given much thought to attracting students, have been spending considerable time toiling over ways to market their schools. They are revamping school logos, encouraging students and teachers to wear T-shirts emblazoned with the new designs. They emphasize their after-school programs as an alternative to the extended days at many charter schools. A few have worked with professional marketing firms to create sophisticated Web sites and blogs.
...

For most schools, the marketing amounts to less than $500, raised by parents and teachers to print up full color postcards or brochures. Typically, principals rely on staff members with a creative bent to draw up whatever they can.

Student recruitment has always been necessary for charter schools, which are privately run but receive public money based on their enrollment, supplemented by whatever private donations they can corral.

The Harlem Success Academy network, run by the former City Council member Eva Moskowitz, is widely regarded, with admiration by some and scorn by others, as having the biggest marketing effort. Their bright orange advertisements pepper the bus stops in the neighborhood, and prospective parents receive full color mailings almost monthly.

Ms. Moskowitz said the extensive outreach was necessary to make sure they were drawing from a broad spectrum of parents. Ms. Moskowitz said they spent roughly $90 per applicant for recruitment. With about 3,600 applicants last year for the four schools in the network, she said, the total amounted to $325,000.

Social norms and happy employees

I came accross the following from from Jay Golz's New York Times blog:

About 10 years ago I was having my annual holiday party, and my niece had come with her newly minted M.B.A. boyfriend. As he looked around the room, he noted that my employees seemed happy. I told him that I thought they were.

Then, figuring I would take his new degree for a test drive, I asked him how he thought I did that. “I’m sure you treat them well,” he replied.

“That’s half of it,” I said. “Do you know what the other half is?”

He didn’t have the answer, and neither have the many other people that I have told this story. So what is the answer? I fired the unhappy people. People usually laugh at this point. I wish I were kidding.

In my experience, it is generally unhappy employees who say things like "But what happens to our business model if home prices go down?" or "Doesn't that look kinda like an iceberg?" Putting that aside, though, this is another example of the principle discussed in the last post -- it's easy to get the norms you want if you can decide who goes in the group.

Charter schools, social norming and zero-sum games

You've probably heard about the Harlem Children's Zone, an impressive, even inspiring initiative to improve the lives of poor inner-city children through charter schools and community programs. Having taught in Watts and the Mississippi Delta in my pre-statistician days, this is an area of long-standing interest to me and I like a lot of the things I'm hearing about HCZ. What I don't like nearly as much is the reaction I'm seeing to the research study by Will Dobbie and Roland G. Fryer, Jr. of Harvard. Here's Alex Tabarrok at Marginal Revolution with a representative sample, "I don't know why anyone interested in the welfare of children would want to discourage this kind of experimentation."

Maybe I can provide some reasons.

First off, this is an observational study, not a randomized experiment. I think we may be reaching the limits of what analysis of observational data can do in the education debate and, given the importance and complexity of the questions, I don't understand why we aren't employing randomized trials to answer some of these questions once and for all.

More significantly I'm also troubled by the aliasing of data on the Promise Academies and by the fact that the authors draw a conclusion ("HCZ is enormously successful at boosting achievement in math and ELA in elementary school and math in middle school. The impact of being offered admission into the HCZ middle school on ELA achievement is positive, but less dramatic. High-quality schools or community investments coupled with high-quality schools drive these results, but community investments alone cannot.") that the data can't support.

In statistics, aliasing means combining treatments in such a way that you can't tell which treatment or combination of treatments caused the effect you observed. In this case the first treatment is the educational environment of the Promise Academies. The second is something called social norming.

When you isolate a group of students, they will quickly arrive at a consensus of what constitutes normal behavior. It is a complex and somewhat unpredictable process driven by personalities and random connections and any number of outside factors. You can however, exercise a great deal of control over the outcome by restricting the make-up of the group.

If we restricted students via an application process, how would we expect that group to differ from the general population and how would that affect the norms the group would settle on? For starters, all the parents would have taken a direct interest in their children's schooling.

Compared to the general population, the applicants will be much more likely to see working hard, making good grades, not getting into trouble as normal behaviors. The applicants (particularly older applicants) would be more likely to be interested in school and to see academic and professional success as a reasonable possibility because they would have made an active choice to move to a new and more demanding school. Having the older students committed to the program is particularly important because older children play a disproportionate role in the setting of social norms.

Dobbie and Fryer address the question of self-selection, "[R]esults from any lottery sample may lack external validity. The counterfactual we identify is for students who are already interested in charter schools. The effect of being offered admission to HCZ for these students may be different than for other types of students." In other words, they can't conclude from the data how well students would do at the Promise Academies if, for instance, their parents weren't engaged and supportive (a group effective eliminated by the application process).

But there's another question, one with tremendous policy implications, that the paper does not address: how well would the students who were accepted to HCZ have done if they were given the same amount of instruction * as they would have received from HCZ using public school teachers while being isolated from the general population? (There was a control group of lottery losers but there is no evidence that they were kept together as a group.)

Why is this question so important? Because we are thinking about spending an enormous amount of time, effort and money on a major overhaul of the education system when we don't have the data to tell us if what we'll spend will wasted or, worse yet, if we are to some extent playing a zero sum game.

Social norming can work both ways. If you remove all of the students whose parents are willing and able to go through the application process, the norms of acceptable behavior for those left behind will move in an ugly direction and the kids who started out with the greatest disadvantages would be left to bear the burden.

But we can answer these questions and make decisions based on solid, statistically sound data. Educational reform is not like climate change where observational data is our only reasonable option. Randomized trials are an option in most cases; they are not that difficult or expensive.

Until we get good data, how can we expect to make good decisions?

* Correction: There should have been a link here to this post by Andrew Gelman.

Instrumental variables

I always have mixed feelings about instrumental variables (at least insofar as the instrument is not randomization). On one hand they show amazing promise as a way to handle unmeasured confounding. On the other hand, it is difficult to know if the assumptions required for a variable to be an instrument are being met or not.

This is a important dilemma. Alan Brookhart, who introduced them into phamracoepidemiology in 2006, has done an amazing job of proving out one example. But you can't generalize from one example and the general idea of using physician preference as an instrument, while really cool, suffers from these assumptions.

Unlike unmeasured confounders, it's hard to know how to test this. With unmeasured confounders you can ask critics to specify what they suspect might be the key confounding factors and go forth and measure them. But instruments are used precisely when there is a lack of data.

I've done some work in the area with some amazing colleagues and I still think that the idea has some real promise. It's a novel idea that really came out of left field and has enormous potential. But I want to understand it in far more actual cases before I conclude much more . . .

Propensity Score Calibration

I am on the road giving a guest lecture at UBC today. One of the topics I was going to cover in today's discussion was propensity score calibration (by the ever brilliant Til Sturmer). But I wonder -- if you have a true random subset of the overall population -- why not just use it? Or, if as Til assumes, the sample is too small, why not use multiple imputation? Wouldn't that be an equivalent technique that is more flexible for things like sub group analysis?

Or is it the complexity of the imputation in data sets of the size Til worked with that was the issue? It's certainly a point to ponder.

Worse than we thought -- credit card edition

For a while it looked like the one good thing about the economic downturn was that it was getting people to pay down their credit card debts. Now, according to Felix Salmon, we may have to find another silver lining:

Total credit-card debt outstanding dropped by $93 billion, or almost 10%, over the course of 2009. Is that cause for celebration, and evidence that U.S. households are finally getting their act together when it comes to deleveraging their personal finances? No. A fascinating spreadsheet from CardHub breaks that number down by looking at two variables: time, on the one hand, and charge-offs, on the other.

It turns out that while total debt outstanding dropped by $93 billion, charge-offs added up to $83 billion — which means that only 10% of the decrease in credit card debt — less than $10 billion — was due to people actually paying down their balances.

Perils of Convergence

This article ("Building the Better Teacher") in the New York Times Magazine is generating a lot of blog posts about education reform and talk of education reform always makes me deeply nervous. Part of the anxiety comes having spent a number of years behind the podium and having seen the disparity between the claims and the reality of previous reforms. The rest comes from being a statistician and knowing what things like convergence can do to data.

Convergent behavior violates the assumption of independent observations used in most simple analyses, but educational studies commonly, perhaps even routinely ignore the complex ways that social norming can cause the nesting of student performance data.

In other words, educational research is often based of the idea that teenagers do not respond to peer pressure.

Since most teenagers are looking for someone else to take the lead, social norming can be extremely sensitive to small changes in initial conditions, particularly in the make-up of the group. This makes it easy for administrators to play favorites -- when a disruptive or under-performing student is reassigned from a favored to an unfavored teacher, the student lowers the average of the second class and often resets the standards of normal behavior for his or her peers.

If we were to adopt the proposed Jack-Welch model (big financial incentitves at the top; pink slips at the bottom), an administrator could, just by moving three or four students, arrange for one teacher to be put in line for for achievement bonuses while another teacher of equal ability would be in danger of dismissal.

Worse yet, social norming can greatly magnify the bias caused by self-selection and self-selection biases are rampant in educational research. Any kind of application process automatically removes almost all of the students that either don't want to go to school or aren't interested in academic achievement or know that their parents won't care what they do.

If you can get a class consisting entirely of ambitious, engaged students with supportive parents, social norming is your best friend. These classes are almost (but not quite) idiot proof and teachers lucky enough to have these classes will see their metrics go through the roof (and their stress levels plummet -- those are fun classes to teach). If you can get an entire school filled with these students, the effect will be even stronger.

This effect is often stated in terms of the difference in performance between the charter schools and the schools the charter students were drawn from which adds another level of bias (not to mention insult to injury).

Ethically, this raises a number of tough questions about our obligations to all students (even the difficult and at-risk) and what kind of sacrifices we can reasonably ask most students to make for a few of their peers.

Statistically, though, the situation is remarkably clear: if this effect is present in a study and is not accounted for, the results are at best questionable and at worst meaningless.

(this is the first in a series of posts about education. Later this week, I'll take a look at the errors in the influential paper on Harlem's Promise Academy.)

Efficacy versus effectiveness

One of the better examples that I have found of this distinction is with physical activity. Travis Saunders talks about the difference between a closely monitored exercise program and encouraging exercise related behavior (despite randomization).

This should be a warning for those of us in drug research as well; not even randomization will help if you have a lot of cross-overs over time or if user tend to alter other behaviors as a result of therapy. This isn't very plausible with some drugs with few side effects (statins) but could be really important for others where the effects can alter behavior (NSAIDs). In particular, it makes me wonder about our actual ability to use randomized experiments of pain medication for arthritis (except, possibly, in the context of comparative effectiveness).

But it is worth thinking about when trying to interpret observational data. What else could you be missing?

Undead papers

Okay, so what do y'all do when a paper becomes undead? We all have work that stopped, for one reason or another, but really needs to be brought to a conclusion. Not even necessarily a happy conclusion (sometimes putting a project out of its misery is the kindest decision for all involved -- especially the junior scientist leading the charge). But sometimes it is the case that the results are just not that compelling (but it still deserves to be published in the journal of minor findings).

But I wonder what is the secret to motivation under these conditions?