Archive for July, 2009
Walk fast to stay ahead of the grim reaper
Mark (in blue) blocked by slow-paced tourists
I added another 10 miles to my Minnesota State Park trail tally this weekend, leaving me only a few more treks short of the century mark and another patch from the Hiking Club.
My idea of a good walk is moving at the briskest pace possible that can be sustained indefinitely. That really gets my blood pumping and thus it is most invigorating. Besides, then I get to more places faster. The tricky part is getting around those who prefer a more leisurely stroll, such as the tourists who impeded my “push hike” to the Mendenhall Glacier outside Juneau, Alaska last year.
Some people I know have questioned my lust for long striding, but a recent report by gerontologists provides support for fast walking – it adds as many as 15 years to one’s life. Specifically, a 74-year old who walks at a gait of 1.4 meters per second (3.1 miles per hour) is more than twice as likely to be alive in 10 years than those oldsters who dawdle at 0.4 m/s (0.9 mph). Now that’s a stat for getting to where you’re going “pdq” (pretty darn quick).*
“Walk steadily and with a purpose. The wandering man knows of certain ancients, far gone in years, who have staved off infirmities and dissolution by earnest walking, hale fellows close upon eighty and ninety, but brisk as boys.”
– Charles Dickens
*Disclaimer: A more logical conclusion is that anyone who can walk this fast at age 74 must be very healthy – possibly just by luck and good genes. Thus, high gait speed is correlated with long life, not the cause of it.
USA health care system “Pareto-inefficient”?
Being a Certified Quality Engineer (CQE) I am well-versed in the Pareto Principle – a term coined by quality guru Joseph Juran for what’s commonly known as the 80-20 rule. When I was the team leader for manufacturing improvement projects, I’d start by categorizing causes for failure and graphing them on an ordered bar chart — most to least, while keeping a running tally on the accumulation in terms of percent. (See this primer on Pareto by the American Society of Quality.) Typically the first 20 percent of causes created 80 percent of the failures – that’s where I first focused the firepower of my quality team.
Today I learned of another concept attributed to the great Italian economist*: Pareto inefficiency. The Concise Encyclopedia of Economics explains that a “Pareto-optimal allocation of resources is achieved when it is not possible to make anyone better off without making someone else worse off.” I found this detailing by The New School which is too much for me to completely digest, but my attention was caught by this heads up:
“An economy can be Pareto-optimal, yet still ‘perfectly disgusting’ by any ethical standards.”
– Harvard Economics Professor Amartya Sen (1970)
So, while I am enticed by the idea that we can make most everyone (80 percent?) better off without making the others (20 percent?) worse off, I remain skeptical. However, having seen what a focused quality improvement team can do with the aid of Pareto charts at a micro level, I remain hopeful that some big strides can be made at the macro level for health care nationwide.
Small sample sizes produce yawning results from sleep studies
Posted by mark in Basic stats & math, design of experiments on July 15, 2009
“Too little attention has been paid to the statistical challenges in estimating small effects.”
— Andrew Gelman and David Weakliem, “Of Beauty, Sex and Power,” American Scientist, Volume 97, July-August 2009 .
In last week’s “In the Lab” column of the Wall Street Journal (WSJ)*, Sarah Rubinstein reported an intriguing study by the “light and health” program of the Rensselaer Polytechnic Institute (RPI). The director, Mariana Figueiro, is trying to establish a lighting scheme for older people that will facilitate their natural rhythms of wakefulness and sleep. In one 2002 experiment (according to WSJ), Dr. Figueiro subjected four Alzheimer patients to two hours of blue, red or no light-emitting diodes (LEDs). After then putting the individuals to bed, their nurses made observations every two hours and found that the “blue-light special” out-did the red by 66% versus 54% on how often they caught patients napping.
Over the years we’ve accumulated many electrical devices in our bedroom – television, cable box, clocks, smoke and carbon monoxide monitors, etc., which all feature red lights. They don’t bother me, but they keep my wife awake. So it would be interesting, I think, if blues would promote snooze. Unfortunately the WSJ report does not provide confidence intervals on the two percentages – nor do they detail the sample size so one could determine statistical significance on the difference of 0.12 (0.66 minus 0.54). (I assume that each of the 4 subjects were repeatedly tested some number of times.) According to this simple calculator posted by the Southwest Oncology Group (a national clinical research group), it would take a sample size of 554 to provide 80% power for achieving statistical significance at 0.05 for this difference!
So, although whether blue light really does facilitate sleep remains questionable, I am comforted by the testimonial of one of the study participants (a 100 years old!) – “It’s a beautiful light,” she says.
PS. Fyi, for more sophisticated multifactor experimentation (such as for screening studies), Stat-Ease posted a power calculator for binomial responses and provided explanation in its June 2009 Stat-Teaser newsletter .
* “Seeking a Light Approach to Elderly Sleep Troubles,” p. D2, 7/7/09
Coriolis effect continues to make the rounds despite efforts to flush it down the drain
Upon hearing a travel report from an acquaintance spending time this summer in Ecuador, I could not resist asking her to observe which way her sink and toilet drained. I’d heard that, due to the Coriolis effect, when you flush water in the northern hemisphere it swirls one way (clockwise), but below the equator it goes the opposite way.* Here is her enthusiastic report:
“Hi Mark, Yesterday I tested it – it´s true! We went to the Mitad del Mundo (Centre of the World), a big monument where the equator line is supposed to be. Unfortunately, they made a mistake when measuring, so the real equator line is a five minute walk away from the monument. By the real line they built a museum and there you can do funny experiments. For example, they put a sink on one side of the equator and let the water flush down, and then they move it to the other side and the water flushes the other way. On the line itself the water just goes straight down – no kidding! It was very interesting!”
I then had to do some research to see if this phenomenon could be independently verified. I hate to be a party pooper (ha, ha!), but, from what I read, in reality the Coriolis effect is so small that it’s easily overwhelmed the shape of the bowl and the other factors. Thus, most toilets flush in only one direction — clockwise or counterclockwise — regardless of location. This is explained very nicely by Alistair B. Fraser, Emeritus Professor of Meteorology Pennsylvania State University, in his white paper on Bad Coriolis.
In any case, it is fascinating to watch the last gallon of water from a hot bath twirl down the drain, so why not observe whether it exits clockwise or counter? I’ve never been south of the equator myself – the nearest I came was in Singapore. My hope is to do some personal validation on the Coriolis effect, or lack thereof. Why not?
*In a memorable episode (I thought it extremely funny) of the television cartoon The Simpsons (16th one in the 6th season), Bart, purporting to be an official with the “International Drainage Commission,” convinces an Australian boy to do a similar ‘down-under’ experiment. The results proved inconclusive, but very humorous. 🙂
Cartoon guides to math & stats
Posted by mark in Basic stats & math on July 5, 2009
In the latest issue of Scientific Computing, Statistician John Wass reviews The Manga Guide to Statistics. He suggests that this simplistic guide may be better suited for middle school than the adult learners it’s aimed at. See for yourself by viewing this excerpt from Chapter 4 of The Manga Guide to Statistics: “Standard Score and Deviation Score” .
I am partial to the Cartoon Guide to Statistics myself. See these sample pages on comparing small sample means . I think this hits the target for those looking for a light refresher on basic stats.
Wass confesses to a “lifelong infatuation” with Walt Disney’s Duck clan, which led me to a movie featurette on Donald in Mathmagic Land, which one can find posted on YouTube and the like. June 25 was the 50th anniversary of its release. Unfortunately, as noted in Wikipedia, a cartoon character states that “Pi is equal to 3.141592653589747, et cetera, et cetera, et cetera.” The last two digits should be 93 – not 47. So the scientist who wrote the script had to eat some humble pi. 😉