Archive for August, 2024
Australia overcomes USA for Olympian heights: Seriously?
Now that Tom Cruise swooped in on the Stade de France outside of Paris and carried off the Olympic flag to Los Angeles, the final reckoning can be made on which country ‘won’ the 2024 Summer Games. I figured that by tying for tops in gold medals and winning the most silver and bronze, the USA was the clear winner.
However, to be fair, one must take population by country into account (within reason by excluding very small countries such as Grenada, who only need to win a few medals top the Olympic chart on a per capita basis). Earlier this year Robert Duncan and Andrew Parece proposed a population-adjusted probability-based index “U”.*
See how your country ranks in by this measure in this final ranking for the Paris Olympics. Aussies rule—gold medals to all! The Peoples Republic of China, who outnumber Australians by 53 to 1, fall to 89th on the list—second to last. Ouch! Kudos to France for coming in second (silver) and Great Britain third (bronze). The USA ranks fifth—not too bad.
Congratulations to all the Olympians and the organizers of this summer’s games for a very entertaining spectacle. Let’s not bogged down by the medal counts—all who participated get full credit for their all-out efforts.
*Per equation 9 in their Journal of Sports Analytics vol. 10, no. 1, pp. 87-104, 2024, research paper on Population-adjusted national rankings in the Olympics
The secret sauce in Guinness beer?
Posted by mark in design of experiments on August 9, 2024
I highly recommend Scientific American’s May 25 Opinion by Jack Murtagh explaining How the Guinness Brewery Invented the Most Important Statistical Method in Science. It nicely illustrates the t test—a landmark statistical method developed by William Sealy Gosset to assess a key ingredient in Guiness beer for ideal bitterness and preservation—soft resin content in hop flowers. Gosset calculated that a 1% difference in the amount of soft resins in the hops, the best and cheapest being purchased from Oregon,* increased their value to the brewery by almost 11%.
“Near the start of the 20th century, Guinness had been in operation for almost 150 years and towered over its competitors as the world’s largest brewery. Until then, quality control on its products had consisted of rough eyeballing and smell tests. But the demands of global expansion motivated Guinness leaders to revamp their approach to target consistency and industrial-grade rigor. The company hired a team of brainiacs and gave them latitude to pursue research questions in service of the perfect brew.”
– Jack Murtagh
Back in 2017 on National Beer Day, celebrated yearly on April 7 to commemorate the end of USA’s prohibition of its sale, I saluted Gosset and his very useful t-test of the significance of one treatment versus another, that is, a simple comparative experiment.**
“They began to accumulate data and, at once, they ran into difficulties because their measurements varied. The effects they were looking for were not usually clearcut or consistent, as they had expected, and they had no way of judging whether the differences they found were effects of treatment or accident. Two difficulties were confounded: the variation was high and the observations were few.”
– Joan Fisher Box,*** “Guinness, Gosset, Fisher, and Small Samples,” Statistical Science, Vol. 2, No. 1 (Feb., 1987), pp. 45-52
To see how the t-test works, check out this awesome graphical app developed Even Miller. Using Stat-Ease software, I cross-checked it against a case study (Example 3.3) from the second edition of Box, Hunter and Hunters’ textbook Statistics for Experimenters. It lays out a simple comparative experiment by a tomato gardener who randomly splits 11 plants for treatment either with her standard fertilizer (A) or a far more expensive one (B) that supposedly produces far better yields. Here are the yield results in pounds, which you can assess using the t test:
- 29.9, 11.4, 25.3, 16.5, 21.1
- 26.6, 23.7, 28.5, 14.2, 17.9, 24.3
On average the new fertilizer increases the yield by nearly 2 pounds, but is the difference statistically significant? That would be good to know! I have the answer, but it would be no fun to tell you, being so easy to find out for yourself.
PS: Due to the large variation between plants (a greater than 6-pound standard deviation!), this tomato study is badly underpowered. If you do an experiment like this, do anything possible to get more consistent results. Then assess power for whatever the difference is that makes changing fertilizers worthwhile. For example, let’s say that with better plant management you got the standard deviation reduced to 3 pounds and a difference of 4 pounds is needed at a minimum to make the switch in fertilizer cost-effective. Then, using Stat-Ease software’s power calculator, I figure you would need to test 3-dozen plants each in your randomized experiment to achieve an 80% probability of detecting a difference of 4 pounds given a 3-pound standard deviation. I hope you like tomatoes!
*As reported by Eat This Podcast in their 4/10/18 post on Guinness and the value of statistics
***I was very fortunate to meet Joan Fisher Box in 2019 as related in this StatsMadeEasy blog/
What not to wear to a dinner hosted by mosquitos
Posted by mark in Nature, Uncategorized on August 2, 2024
Yesterday I stopped by Minnesota’s Metropolitan Mosquito Control District (MMCD) booth at our local county fair. They display live mosquito larvae swimming in a shallow pan of water. Visitors can pipette them on to a slide and view them with a microscope. Fascinating!
Thanks to the mosquito control services by MMCD (and/or developments reducing habitat) I’ve seen a dramatic decrease in these pests since moving into my home in Stillwater almost 30 years ago. However, there were plenty of ‘skeeters at the Anderson family get-together up north at Pine Terrace Resort last month. While packing for our getaway, my wife advised that to be less attractive to these flying insects I bring white or lightly colored clothes and none with any reds. Being a professional skeptic of such assertions, I immediately looked for any science to support her advice. As usual, she was right, as you can see in this 2022 publication by Nature on The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes.
If you are put off by too much information, watch this LIVENOW interview of co-author Jeffrey A. Riffell—a biology professor at the University of Washington, Seattle. I like his heads-up that mosquitos learn not to bite people swatting them away and go for easier prey. In other words, if you are going for a hike in the woods, bring along someone who would rather get bitten up than look like a city slicker. Then diligently swat all mosquitos over to your trail-mate—better to look like a fool than be bitten-upped cool.
PS: I am a big fan of DEET repellants for deterring mosquitos and, equally important, ticks. I also wear a cap treated with permethrin, which is a real game changer as advised by Hiking Thru Life. Of course, in areas where mosquitos gather in visible clouds, covering up completely, starting with a head net, is the only way to go. Given the huge increase in mosquito-borne and tick-borne diseases in the United States and elsewhere, it’s best to “fight the bite”.