Comments, observations and thoughts from two bloggers on applied statistics, higher education and epidemiology. Joseph is an associate professor. Mark is a professional statistician and former math teacher.
Friday, June 4, 2010
How is war like comedy?
That's the only thing in the post you can dismiss. The rest of it is sharp, on-target and pretty much essential reading if you're following the education debate.
Thursday, June 3, 2010
Really not that damned funny
Today's New York Times has a reminder of what the cost of blights and pests can be:
Lynet Nalugo dug a cassava tuber out of her field and sliced it open.
Inside its tan skin, the white flesh was riddled with necrotic brown lumps, as obviously diseased as any tuberculosis lung or cancerous breast.
“Even the pigs refuse this,” she said.
The plant was what she called a “2961,” meaning it was Variant No. 2961, the only local strain bred to resist cassava mosaic virus, a disease that caused a major African famine in the 1920s.
But this was not mosaic disease, which only stunts the plants. Her field had been attacked by a new and more damaging virus named brown streak, for the marks it leaves on stems.
That newcomer, brown streak, is now ravaging cassava crops in a great swath around Lake Victoria, threatening millions of East Africans who grow the tuber as their staple food.
Although it has been seen on coastal farms for 70 years, a mutant version emerged in Africa’s interior in 2004, “and there has been explosive, pandemic-style spread since then,” said Claude M. Fauquet, director of cassava research at the Donald Danforth Plant Science Center in St. Louis. “The speed is just unprecedented, and the farmers are really desperate.”
Two years ago, the Bill and Melinda Gates Foundation convened cassava experts and realized that brown streak “was alarming quite a few people,” said Lawrence Kent, an agriculture program officer at the foundation. It has given $27 million in grants to aid agencies and plant scientists fighting the disease.
The threat could become global. After rice and wheat, cassava is the world’s third-largest source of calories. Under many names, including manioc, tapioca and yuca, it is eaten by 800 million people in Africa, South America and Asia.
Maybe it's just me but I really don't see what's so funny about agricultural research. Perhaps Maureen can explain it to me.
Wednesday, June 2, 2010
"The upside of mortgage default"
"Poll: Only Campbell Can Beat Boxer"
The poll by the Los Angeles Times and University of Southern California clearly shows that U.S. Sen. Barbara Boxer is unpopular with voters, but in a theoretical matchup, only one of the three GOP primary candidates can beat her: former Silicon Valley congressman Tom Campbell.As mentioned before, the GOP primary process is broken.But the poll also indicates that Campbell might not have the chance to face Boxer: Former Hewlett-Packard CEO Carly Fiorina has a huge lead in the three-way primary contest to decide which Republican will run against Boxer in the fall.
Resisting the urge to make a bad pun here
Perils of Cross-sectional Studies
For example, risk taking behavior is u-shaped (highest for the wealthy and the permanently indebted). I can't tell if this relationship in her data is statistically significant (as the variance is not presented) but that doesn't get at the main point, anyway.
The main point is that you would expect people who take risks to break into the highly successful and the impoverished. Looking at the final outcome and saying "what is the expected value of taking risks" is more informative than noting risk takers have more money. If somebody offered to double your wealth if you could roll a 1 or a 2 on a 6 sided die, would this be a good idea? Yet, if we offered this choice to a room of people and then ranked them by net worth, it's likely that the wealthiest people would have rolled the die. So would the least wealthy, as well.
What if you doubled your income on a 1 to 4; the expected value of the roll is positive but losing everything you own might be worse than doubling what you currently have. It's a very complicated inference and it probably requires a posterior distribution to properly express what the choices look like.
Now, I suspect that prospective data would support intelligent risk taking and the book has a lot of good data in it (so don;t take this as a slam of the book as a whole; actually gathering and interpreting data adds a lot to the conversation even if the interpretation isn't always trivial). But it does highlight the complexity of drawing any inferences from cross-sectional retrospective studies. It's not just an issue with Epidemiology data but can occur anywhere else.
[note: some typos were corrected after the initial posting]
Tuesday, June 1, 2010
Journal Selection Strategy
Is this worse if you are an early career scientist who needs to get their work out their to establish productivity?
I have actually had this happen where a paper got mostly positive reviews, a major revision and then an ultimate rejection. The process took a very long time and the final dismissal was a single sentance. It's was a nasty enough experience that it actually makes me reluctant to return to that journal again.
Would I do it again? Maybe . . . After that, I dramatically undershot the next choice of journal for a potentially controversial paper. This was also a major mistake. The hardest cases are alwasy going to be the borderline ones. Long review times and ambiguous options to resubmit are always a bad outcome, no matter how I look at it.
But I wish I had a better feel for what the risk/benefit trade-off really was . . .
Monday, May 31, 2010
Robert Samuelson would not make a good statistician
Here's the quote from Samuelson:
Second, the poor's material well-being has improved. The official poverty measure obscures this by counting only pre-tax cash income and ignoring other sources of support. These include the earned-income tax credit (a rebate to low-income workers), food stamps, health insurance (Medicaid), and housing and energy subsidies. Spending by poor households from all sources may be double their reported income, reports a study by Nicholas Eberstadt of the American Enterprise Institute. Although many poor live hand-to-mouth, they've participated in rising living standards. In 2005, 91 percent had microwaves, 79 percent air conditioning and 48 percent cellphones.The fallacy here is closely related to the phenomena of the wrong-way coefficient. You fit a model and you see a statistically significant variable with the wrong sign. For a fairly silly example, you build a model predicting how long it takes travellers to get from New York City to DC and you find that the indicator for being searched by a uniformed officer has a negative coefficient which would suggest that being searched somehow shortens your travel time. The explanation for this counterintuitive result is that there's a relationship between this variable and one or more of the other variables in your model. In this case there's a strong correlation between being searched and flying vs. driving.
For people living in residences with functioning kitchens, good ventilation and a land line, getting a microwave, an air conditioner and a prepaid cellphone clearly represents an increase in well being. If, however, there is an inverse relationship among the poor between having a stove/having a microwave, or ventilation/AC or land line/cell, then the high incidence rates could easily indicate a lower standard of living.
So many immigrants, homeless people and others of limited means living in single-room occupancies (SROs) have no kitchens, no legal or official place to cook. To get a hot meal, or eat traditional foods from the countries they've left behind, they have to sneak a kind of kitchen into their places. Crock pots, hot plates, microwaves and toaster ovens hidden under the bed. And now, the latest and safest appliance, the appliance that comes in so many colors it looks like a modern piece of furniture: the George Foreman Grill. It is, quite literally, a hidden kitchen.
Network TV -- now entering their fourth decade on death's door
YouTube’s viewership now exceeds that of all three networks combined during their “primetime” evening time slot, with more than 2 billion views per day, Google announced Sunday.
There are a lot of statistical flaws in the article but the one that jumped out at me was the bit about "all three networks." This is a particularly embarrassing variation on an old fallacy. Articles on the decline of network viewership have often failed to take new networks into account, for example comparing CBS/ABC/NBC viewership in 1980 and 1995 then concluding that the difference represented people going to cable.
You can see how someone would make that mistake. It seems to be an apples-to-apples comparison even though it's not.
But in a discussion limited strictly to 2010 viewership, talking about "all three networks" is just weird.
The economics of rock and roll part III -- Gimme (tax) Shelter
The image may be rebellious and unkempt, but the reality is that the Rolling Stones are very smart when it comes to money. On worldwide earnings of $150 million last year they paid just 1.5 percent in tax.
The details have emerged under Dutch law. The band's financial advisers apparently have offices in a Dutch tax haven. The lightness of the Stones' tax burden is not a surprise, says former rock musician Neil MacCormick:NEIL MACCORMICK: They're a big machine. They've probably learned the hard way, and learned on the road how to protect their money.He says world tours are usually organized according to tax rules, with a band rarely appearing for longer than 30 days in each country.
The economics of rock and roll part II -- quality control and brown M&Ms
From Snopes:
The legendary "no brown M&Ms" contract clause was indeed real, but the purported motivation for it was not. The M&Ms provision was included in Van Halen's contracts not as an act of caprice, but because it served a practical purpose: to provide an easy way of determining whether the technical specifications of the contract had been thoroughly read (and complied with). As Van Halen lead singer David Lee Roth explained in his autobiography:Van Halen was the first band to take huge productions into tertiary, third-level markets. We'd pull up with nine eighteen-wheeler trucks, full of gear, where the standard was three trucks, max. And there were many, many technical errors — whether it was the girders couldn't support the weight, or the flooring would sink in, or the doors weren't big enough to move the gear through.
The contract rider read like a version of the Chinese Yellow Pages because there was so much equipment, and so many human beings to make it function. So just as a little test, in the technical aspect of the rider, it would say "Article 148: There will be fifteen amperage voltage sockets at twenty-foot spaces, evenly, providing nineteen amperes . . ." This kind of thing. And article number 126, in the middle of nowhere, was: "There will be no brown M&M's in the backstage area, upon pain of forfeiture of the show, with full compensation."
So, when I would walk backstage, if I saw a brown M&M in that bowl . . . well, line-check the entire production. Guaranteed you're going to arrive at a technical error. They didn't read the contract. Guaranteed you'd run into a problem. Sometimes it would threaten to just destroy the whole show. Something like, literally, life-threatening.
The economics of rock and roll
I ran this by the music historian Brad Kay, who confirmed that Jagger had his facts right. Thanks to Tyler for posting this and more thanks to Gut(?) who commented:Jagger, of course, studied economics at LSE and is known to be a fan of Hayek....people only made money out of records for a very, very small time. When The Rolling Stones started out, we didn’t make any money out of records because record companies wouldn’t pay you! They didn’t pay anyone!
Then, there was a small period from 1970 to 1997, where people did get paid, and they got paid very handsomely and everyone made money. But now that period has gone.
So if you look at the history of recorded music from 1900 to now, there was a 25 year period where artists did very well, but the rest of the time they didn’t.
He is also the primary datapoint for the observation that economists do it with models.
Elegance and Economics -- a choice comment from Paul Krugman
Few economists saw our current crisis coming, but this predictive failure was the least of the field’s problems. More important was the profession’s blindness to the very possibility of catastrophic failures in a market economy. During the golden years, financial economists came to believe that markets were inherently stable — indeed, that stocks and other assets were always priced just right. There was nothing in the prevailing models suggesting the possibility of the kind of collapse that happened last year. Meanwhile, macroeconomists were divided in their views. But the main division was between those who insisted that free-market economies never go astray and those who believed that economies may stray now and then but that any major deviations from the path of prosperity could and would be corrected by the all-powerful Fed. Neither side was prepared to cope with an economy that went off the rails despite the Fed’s best efforts.
And in the wake of the crisis, the fault lines in the economics profession have yawned wider than ever. Lucas says the Obama administration’s stimulus plans are “schlock economics,” and his Chicago colleague John Cochrane says they’re based on discredited “fairy tales.” In response, Brad DeLong of the University of California, Berkeley, writes of the “intellectual collapse” of the Chicago School, and I myself have written that comments from Chicago economists are the product of a Dark Age of macroeconomics in which hard-won knowledge has been forgotten.
What happened to the economics profession? And where does it go from here?
As I see it, the economics profession went astray because economists, as a group, mistook beauty, clad in impressive-looking mathematics, for truth. Until the Great Depression, most economists clung to a vision of capitalism as a perfect or nearly perfect system. That vision wasn’t sustainable in the face of mass unemployment, but as memories of the Depression faded, economists fell back in love with the old, idealized vision of an economy in which rational individuals interact in perfect markets, this time gussied up with fancy equations. The renewed romance with the idealized market was, to be sure, partly a response to shifting political winds, partly a response to financial incentives. But while sabbaticals at the Hoover Institution and job opportunities on Wall Street are nothing to sneeze at, the central cause of the profession’s failure was the desire for an all-encompassing, intellectually elegant approach that also gave economists a chance to show off their mathematical prowess.
Sunday, May 30, 2010
Distributed computing
However, even if I could, I doubt that I would in the absence of brutally complete back-ups (which would rather eliminate any space savings). Because the world is broken up into two groups of people: those who have lost data due to crashes and those who are yet to do so. When you are in the former group, it seems the height of insanity not to be as a careful as possible about keeping data safe.
Heck, I dislike how the SAS program editor does not have an autosave feature. I've lost code because I walked away from the computer for a meeting and windows decided that was an ideal time for an auto-update. In that sense, the static environment of using the computer as a tool is at war with the dynamic vision of computer developers.
I wonder if, at some point, we'll branch off into two streams? Computers are cheap enough that you no longer need one platform for everything and I mostly use the internet at work for downloading articles (a function that slowly updated libraries could pretty much handle).
It is an interesting thought.