Posts Tagged regression
Too many dogs at farmers markets?
Today’s “Gray Matter” column in the New York Times provides an exceptionally well-balanced report that casts doubt on the healthiness of food from farmers markets—read it here. What caught my eye is how the author, a professor at University of Minnesota (my alma mater), lays out a number of positive correlations (being careful not to conclude causation) between farmers markets and various food-borne illnesses, including one attributed to the ‘droppings’ from dogs and the like. But the thing I most admire is him admitting to “a number of dogs that did not bark”, i.e., a number of outbreaks that did not show a statistically significant connection to farmers markets.
This suggestion of possible health issues with farmers markets is heavily hedged—very possibly it will not be borne out by subsequent research. Nevertheless it would only be prudent to thoroughly wash locally grown and sold produce.
Why coaches regress to be mean
Posted by mark in Consumer behavior on June 13, 2011
In a column for Newsweek magazine, science writer Sharon Begley* discusses how ignorance about the statistical principle of regression to the mean** causes all sorts of crazy behavior. For example, sufferers of colds try a new remedy that seems to make them better, but in reality, they were already recovering. This behavior leads to over-use of antibiotics, which breeds drug-resistant bacteria. Ultimately, according to this quote passed along by Begley:
“People die at a biblical scale because of such stupidity.”
– Ben Goldacre, author of Bad, Science: Quacks, Hacks and Big Pharma Flacks.
On a lighter (?) note, this tendency by people to attribute cause-and-effect relationships to random ups-and-downs explains why some teachers, coaches and instructors hold back praise and only berate their pupils. A case in point is the flight instructor who lavishes praise on a training-pilot who makes a lucky landing. Naturally the next result is not so good. Later the pilot bounces in very badly — again purely by chance (a gust of wind). The instructor roars disapproval. That seems to do the trick — the next landing is much smoother. So now you know why coaches yell so much: It’s their regression to the mean.
* “Wanted: BS Detectors” – 11/8/10.
**First brought forward by France Galton in 1886 via this essay on “Regression towards Mediocrity in Hereditary Stature”
Political science (?) based on happenstance regression
My daughter Carrie, a junior at University of Minnesota — majoring in political science, asked me to look over a paper she wrote last week for her quantitative-analysis class. Her assignment was to test “the theory that Christian religiosity, measured through church attendance, affected the outcome of the 2004 presidential election” (Bush over Kerry). Carrie considered many other variables that could logically have influenced voting decisions before settling on two alternative factors – per-capita income, and level of education.
As I’d expected, her regression analysis (using the SPSS software) showed a positive correlation of “frequent church goers” voting for Bush (0.166 R2) and negative for “population with college degree or higher” (0.293). However, the highest correlation was seen with per-capita income, which surprised me by being negative – the more the voter earned, the more likely they were to NOT vote for Bush. I always thought that the Republicans were the party of the rich. But from this data one must conclude that they mainly appeal to poor, less-educated church-goers! (Please do not take the previous two ‘tongue-in-cheek’ statements seriously, I am only making a humorous point about how misleading statistics can be!)
I don’t give too much credence to any of this – mainly due to my great skepticism of using statistics to dissect historical data and generate inferences on cause and effect relationships. However, it makes me curious as to the driving forces of today’s party politics in the USA. That’s about all I figure that regression of happenstance data really offers – some food for thought that may lead to more rigorous investigation.