Archive for category Uncategorized
Smooth sliding for 2011
Posted by mark in Uncategorized on January 1, 2011
Here’s hoping you enjoy smooth sliding in 2011 like I did recently outside my front door.
Happy New Year!
– Mark
PS. Kudos for my daughter Emily for this production.
Fishing for giant snakes with a boy as bait
Posted by mark in Uncategorized on November 28, 2010
The statistics are:
- Prey: Length 26 feet, weight 320 pounds
- Predator: Length 4 feet (?), weight 90 pounds.
Here in Minnesota we love to tell fishing stories that can be real whoppers, but this one told by Everglades Outpost founder Bob Freer beats all. I heard the story yestesterday on National Public Radio’s “Wait Wait… Don’t Tell Me” show.* Freer and his crew were confounded by a very large snake lurking under a house – the hole would not admit a full-grown adult. Luckily a kid watching the proceedings stepped up to help. The snake hunters tied a rope to his leg and handed him a stick with a napkin tied to it. With the 90-pound boy (brave or foolhardy?) as bait, they fished out a 26-foot long, 320 pound reptile – a python, I presume.**
“We told him to make sure not to tell his mother.”
– Bob Freer
PS. Pictured here in my hand is a Ball python – a popular pet due to being so small (several feet in length and a few pounds at most) in addition to their endearing eponymous tendency to curl up into a comfortable coil.
* See the transcript of “Animal Expert Bob Freer Plays Not My Job” here
** The National Park Service just released their latest statistics on the proliferation of Burmese pythons in the Everglades – see the year-by-year count here.
Prof applies stats to flush out widespread cheating
Posted by mark in Uncategorized on November 24, 2010
See this recent ABC News report on how perhaps as many as 200 University of Central Florida (UCF) students cheated on an exam. The YouTube video of them being accused by the teacher, armed with supporting statistical detail and an actual confession, can be seen here.
“This is what’s called a bimodial distribution… [which].. exists when an external force has been applied… that creates a systematic bias.”
– Professor Richard Quinn describing a histogram of scores from his mid-term test for University of Central Florida Strategic Management 4720
For some alarming stats on percent of students cheating (mostly reported to be well over half!), see this summary of surveys on exam-beaters compiled by a test-security firm (but consider the probability of them being a bit biased!).
Getting back to Professor Quinn, I am amazed at how many commentors blame him for not updating his exams. Evidently students cannot be held accountable for cheating when it is so easy to accomplish. 🙁
“This is college. Everyone cheats, everyone cheats in life in general.”
– CSU student Konstantin Ravvin
Pigging out in Italy – a 30-meter pork roast
Posted by mark in Uncategorized, Wellness on November 21, 2010
We are gathering quantities of food for a Thanksgiving feast at the Anderson home this Thursday. As my stomach rumbles* in anticipation, my thoughts turn to another great feast that I saw prepared last summer in Bergamo, Italy.** There they prepared pork (or porchetta, as they say), rather than the turkey we prefer in the New World. What made this Bergamo barbecue so singular was the way the cooked their pigs – sewn together into a 30 meter roast! See the results in this video I took (produced by my daughter Emily).
A meter or two of this porchetta would be the perfect warm up for our Thanksgiving banquet. I wonder what these Italians would do to dress up a turkey. They sure know how to create a spectacle!
*In medical terms known as “borborygmi” – a normal symptom of hunger.
**See this report
Election day pits pollsters as well as politicians
Posted by mark in politics, Uncategorized on November 2, 2010
Sunday’s St. Paul Pioneer Press reported* an astounding range of predictions for today’s election results for Governor of Minnesota. The Humphrey Institute showed Democrat Dayton leading Republican Emmer by 41 to 29 percent, whereas Survey USA (SUSA) respondents favored Dayton by only 1 percent – 39-38! The SUSA survey included cell-phone-only (CPO) voters for the first time – one of many factors distinguishing it from their competitor for predicting the gubernatorial race.
What I always look for along with such predictions is the margin of error (MOE). The Humphrey Institute pollsters provide these essential statistical details: “751 likely voters living in Minnesota were interviewed by telephone. The margin of error ranges between +/-3.6 percentage points based on the conventional calculation and +/-5.5 percentage points, which is a more cautious estimate that takes into account design effects, in accordance with professional best practices.”** Note that the more conservative MOE (5.5%) still left Dayton with a significant lead, but just barely at 12 points (vs 5.5%x2 = 11% overlap of MOEs).
Survey USA, on the other hand, states their MOE as +/- 4%. They provide a very helpful statistical breakdown by CPO versus landline, gender, age, race, etc. at this web posting. They even include a ‘cross-tab’ on Tea Party Movement – a wild card in this year’s election.
By tomorrow we will see which polls get things right. Also watching results with keen interest will be the consultants who advise politicians on how to bias voters their way. Sunday’s New York Times offered a somewhat cynical report on how these wonks “Nudge the Vote”. For example, political consultant Hal Malchow developed a mailer that listed each recipient’s voting history (whether they bothered to do so, or not), along with their neighborhood (as a whole, I presume). Evidently this created a potent peer pressure that proved to be 10 times more effective in turning non-voters into voters! However, these non-intuitive approaches stem from randomized experiments, which require a control group who get no contacts (Could I volunteer to be in this group?). This creates a conundrum for political activists – they must forego trying to influence these potential voters as the price paid for unbiased results!
“It’s the pollsters that decide. Well, a poll can be skewered [sic #]. I can go out and get you a poll on anything you want and probably get the results that I want just in how I conduct it.”
— Jesse Ventura, professional wrestler (“The Body”) and former governor of Minnesota
# Evidently a Freudian slip – him being skewered on occasion by biased polls. 😉
* “Poll parsing” column by David Brauer, page 15B.
Brain-bending thoughts on a coffee experiment
Posted by mark in design of experiments, Uncategorized, Wellness on October 24, 2010
The Stat-Ease training center here at our world headquarters in Minneapolis features a wonderful single-cup brewing system that you can see demoed here. When we are not holding a workshop, I sometimes sneak in to steal a cup late in the day. By then I am reaching my limit, so I brew a “half-calf” at the half-cup setting. Being a chemical engineer, I calculate that, in this case, half of half makes a whole, that is, coffee with the normal concentration of caffeine. Does that make sense?
Making a tasty and effective cup of coffee is a huge deal for knowledge workers who need to keep their heads in gear from start to finish of every single day. One of our workshop students, a PhD, has been picking my brain about testing coffee blends on her staff of scientists. She proposes to do a mixture design such as I did on varying types of beers (see Mixture Design Brews Up New Beer Cocktail—Black & Blue Moon).
Obviously overall liking on a sensory basis should be first and foremost for such an experiment on coffee – a 5 to 9-point scale works well for this.* However, the tricky part is assessing the impact of coffee for accelerating information processing and general problem-solving, which I hypothesize depends on level of caffeine. I wonder if an online “brain training” service, such as this one developed by neuroscientists at Stanford and UCSF, might provide a valid measure.
The down side of doing a proper test on whether coffee improves cognitive skills will be the necessity of reverting to the base line, that is, every morning getting up and trying to function without the first cup.
“A mathematician is a machine for turning coffee into theorems.”
— Alfréd Rényi
*Turn your volume down (to not hear the advert) and see this primer on sensory evaluation by S-Cool– a UK educational site for teenagers.
Yankees leverage wins by throwing money at their players
Posted by mark in sports, Uncategorized on September 26, 2010
Today’s New York Times sports section provided this intriguing graphic on “putting a price tag on winning”. Their hometown Yankees stand out as the big spenders by far. It paid off in wins over the last decade – the period studied. However, if you cover up the point depicting the Yanks, the graph becomes far less compelling that salary buys wins – mainly due to counteractive results enjoyed by two low-payroll teams: The Minnesota Twins and the Oakland Athletics.
I found similar patterns and, more importantly, data to reproduce these, in this study of MLB Payroll Efficiency, 2006-2008 by Baseball Analyst Rich Lederer.
No offense to Rich or the NY Times – it is the damn Yankees (sorry but I am weary of them defeating the Twins every post-season) who are the blame for this flaw in drawing conclusions from this data: One point exerts undue leverage on the fit, which you can see on this diagnostic graph generated by Design-Expert® software.
However, after doing the obvious thing – yanking the Yanks from the data, the conclusion remains the same: Higher payroll translates to more wins in Major League baseball. Here are the stats with/without the Yankees:
- R-squared: 0.41/0.34
- Wins per $ million of payroll (slope of linear fit): +0.13/0.16
In this case, a high leverage point does not exert the potential influence, that is, the end result does not change due to its location. If you’d like to simulate how leverage impacts fit, download this educational simulation posted by Hans Lohninger, Associate Professor of Chemometrics at Vienna University of Technology.
Minnesota’s ’08 Senate race dissed by British math master Charles Seife
Posted by mark in Basic stats & math, politics, Uncategorized on September 20, 2010
Sunday’s New York Times provided this review of Proofiness – The Dark Arts of Mathematical Deception – due for publication later this week. The cover, seen here in Amazon, depicts a stats wizard conjuring numbers out of thin air.
What caught my eye in the critique by Steven Strogatz – an applied mathematics professor at Cornell, was the deception caused by “disestimation” (as Proofiness author Seife terms it) of the results from Minnesota’s razor-thin 2008 Senate race, which Al Franken won by a razor-thin 0.0077 percent margin (225 votes out of 1.2 million counted) over Norm Coleman. Disestimation is the act of taking a number too literally, understating or ignoring the uncertainties that surround it; in other words, giving too much weight to a measurement, relative to its inherent error.
“A nice anecdote I like to talk about is a guide at the American Museum of Natural History, who’s pointing at the Tyrannosaurus rex. Someone asks, how old is it, and he says it’s 65 million and 38 years old. Sixty-five million and 38 years old, how do you know that? The guide says, well, when I started at this museum 38 years ago, a scientist told me it was 65 million years old. Therefore, now it’s 65 million and 38. That’s an act of disestimation. The 65 million was a very rough number, and he turned it into a precise number by thinking that the 38 has relevance when in fact the error involved in measuring the dinosaur was plus or minus 100,000 years. The 38 years is nothing.”
– Charles Seife (Source: This transcript of an interview by NPR.)
We Minnesotans would have saved a great deal of money if our election officials had simply tossed a coin to determine the outcome of the Franken-Coleman contest. Unfortunately, disestimation is embedded in our election laws, which are bound and determined to make every single vote count, even though many thousands in a State-wide race prove very difficult to decipher.
Quantifying statements of confidence: Is anything “iron clad”?
Posted by mark in Basic stats & math, Uncategorized on August 19, 2010
Today’s “daily” emailed by The Scientist features a heads-up on “John Snow’s Grand Experiment of 1855” that his pioneering epidemiology on cholera may not be as “iron clad” as originally thought. A commentator questions what “iron clad” means in statistical terms.
It seems to me that someone ought to develop a numerical confidence scale along these lines. For example:
- 100% Certain.
- 99.9% Iron clad.
- 99% Beyond a shadow of a doubt.
- 95% Unequivocal.
- 90% Definitive.
- 80% Clear and convincing evidence.
- 50% On the balance of probabilities.
There are many other words used to convey a level of confidence, such as: clear-cut, definitive, unambiguous, conclusive. How do these differ in degree?
Of course much depends on how is making such a statement, many of whom are not always right, but never in doubt. ; ) I’m skeptical of any assertion, thus I follow the advice of famed statistician W. Edwards Deming:
“In God we trust, all others bring data.”
Statistics can be very helpful for stating any conclusion because it allows one to never have to say you are certain. But are you sure enough to say it’s “iron clad” or what?
Blah, blah, blah…”quadratic”
Posted by mark in design of experiments, Uncategorized on August 15, 2010
This add by Target got my attention. It reminded me of my futile attempt to get my oldest daughter interested in math. For her the last straw was my overly-enthusiastic reaction to her questioning me why anyone would care about quadratic equations. Perhaps I over-reacted and lectured on a bit too long about this being a very useful approximating function for response surface methods, blah, blah, blah…