Month: December 2012

Few Doctors Understand Statistics?

Seth Roberts16 Comments

A few days ago I wrote about a study that suggested that people who’d had bariatric surgery were at much higher risk of liver poisoning from acetaminophen than everyone else. I learned about the study from an article by Erin Allday in the San Francisco Chronicle. The article included this:

At this time, there is no reason for bariatric surgery patients to be alarmed, and they should continue using acetaminophen if that’s their preferred pain medication or their doctor has prescribed it.

This was nonsense. The evidence for a correlation between bariatric surgery and risk of acetaminophen poisoning was very strong. Liver poisoning is very serious. Anyone who’s had bariatric surgery should reduce their acetaminophen intake.

Who had told Allday this nonsense? The article attributed it to “the researchers” and “weight-loss surgeons”. I wrote Allday to ask.

She replied that everyone she’d spoken to for the article had told her that people with bariatric surgery shouldn’t be alarmed. She did not understand why I considered the statement (“no need for alarm”) puzzling. I replied:

The statement is puzzling because it is absurd. The evidence that acetaminophen is linked to liver damage in people with bariatric surgery is very strong. Perhaps the people you spoke to didn’t understand that. The size of the sample (“small”) is irrelevant. Statisticians have worked hard to be able to measure the strength of the evidence independent of sample size. In this case, their work reveals that the evidence is very strong.

If the experts you spoke to (a) didn’t understand statistics and (b) were being cautious, that would be forgivable. That’s not the case here. They (a) don’t understand statistics and (b) are being reckless. With other people’s health. It’s fascinating, and very disturbing, that all the experts you spoke to were like this.

I have no reason to think that the people Allday talked to were more ignorant than typical doctors. I expect researchers to be better at statistics than average doctors. One possible explanation of what Allday was told is that most doctors, given a test of basic statistical concepts, would flunk. Not only do they fail to understand statistics, they don’t understand that they don’t understand. Another possible explanation is that most doctors have a strong “doctors do everything right” bias, even when it endangers patients. Either way, bad news.

Why Do Fermented Foods Improve Health? A New Idea

Seth Roberts11 Comments

I became interested in the health value of fermented foods after I noticed a curious coincidence. Humans have three mysterious food preferences: for (a) sour food, (b) food with umami flavor, and (c) food with complex flavor. I realized that all three preferences made bacteria-laden food more attractive. Bacteria change sugars to acids, increasing sourness. They break down proteins, creating glutamate, which produces umami flavor. And the many chemicals they introduce into a food make its flavor more complex. After I noticed this, I came across many studies that supported the idea that fermented foods are good for health. I also found studies that suggest the bacteria in our digestive system are crucial to health.

This raised the question: What fermented foods to eat? How many? How often? To begin to answer these questions, it would help to know how bacteria in our food help us be healthy. There were two obvious answers:

1. Stimulate the immune system. The bacteria in fermented food are inherently safe: they are specialized to reproduce on/in food, which is so different than inside the human body. But the immune system doesn’t know this. If this was one benefit of fermented food, you could study which ones to eat by measuring immune system activation. Unfortunately, that is nearly impossible.

2. Improve digestion. Many people have digestive problems and some of them are helped by fermented foods. Obviously they contain bacteria that digest food. I don’t have digestive problems so I can’t study this by figuring out which fermented foods help.

Recently, I have begun to think there is a third reason:

3. Place competition. To make us sick, outside bacteria need to stick inside us. To digest our food, the surfaces of our digestive system, such as the inside of our intestines, is much more porous than other surfaces, such as our skin. It is our digestive system, therefore, that is most vulnerable to dangerous microbes. The totally-safe microbes in fermented foods compete for sticky spots with other, more dangerous microbes. If there are plenty of safe bacteria — say, billions in a serving of yogurt — they may do a lot to protect us against the dozen or so similar dangerous bacteria we might get from touching the same surface as a sick person. I think of a wooden floor where the lumber is not quite well-fitted. If you want to protect what’s below that floor from black sand (dangerous), an excellent method would be to pour an enormous amount of white sand (safe) on the floor.

If Effect #3 (place competition) is the main reason fermented food protects us from disease, it implies that dead bacteria work as well as live bacteria (in contrast, live bacteria do not digest food, Effect #2). This might explain the potency of alcoholic beverges such as wine, where most of the bacteria are dead. It also suggests that what matters is diversity of where bacteria stick and how much they stick. It might someday be possible to feed people (non-radioactive) bacteria and learn where in the body they end up.

 

 

Online Teaching Versus What?

Seth Roberts12 Comments

Is online teaching (e.g., MOOC) a big deal? In an essay (“Why Online Education Works”), Alex Tabarrok argues for the value of online education (meaning online lectures) compared to traditional lectures. A friend told me yesterday that MOOC was “a frontier of pedagogy”. No doubt online lectures will make lecture classes cheaper and more available. Lots of things have gone from scarce/expensive to common/cheap. With things whose effects we understand (e.g., combs), the result is straightforward: more people benefit. With things whose effects we don’t understand, the results are less predictable. Did the spread of sugar help us? Hard to say. Did the spread of antibiotics help us? Hard to say. It may have helped sustain simplistic ideas about what causes disease (e.g., “acne is caused by bacteria”, “ulcers are caused by bacteria”) reducing effective innovation. Do we have a good idea of the effects of lectures (or their lack of effect), or a good theory of college education? I don’t think so. Could their spread help sustain simplistic ideas about education? Maybe.

As books spread, the teaching of reading increased. Everyone understood that books were useless if people couldn’t read. The introduction of PCs was accompanied by user interface improvements. This helped PCs become influential– not restricted to hobbyists. Will online education be accompanied by similar make-it-more-palatable changes? I have heard nothing about this. Their advocates seem to think the current system is fine and if it could only be available to more people…

Online lectures will make much difference only if the cost and quality of lectures is the weakest link in what strikes me as a process with many links. It would be a coincidence if the link that can be most easily strengthened turned out to be the weakest link. For example, is the cost of lectures the main thing driving up the cost of college? That would be wonderful if it were true, but I haven’t seen evidence that it’s true. At Berkeley, for example, there has been enormous growth in the administrator-to-faculty ratio.

Here are two arguments used to argue that online lectures are a big step forward:

It will help people in poor countries, like Zambia. There is a long history of people in rich countries misunderstanding people in poor countries. Several years ago I was in Guatemala. I heard about a school being built by a (rich country) religious group in a poor area. After two years, the American running it wanted to leave. No member of the community took it over. It disappeared. “Maybe they didn’t want a school,” said the graduate student who told me about it. Maybe few people in Zambia want online lecture classes. (I have no idea.) If so, the benefit will be small.

It will save labor. Each lecture will be viewed many more times. Saving labor is not always good. It is plausible that the growth of online lectures will mean fewer college professors. Colleges and universities are among the few places where people do research and almost the only places where they do unrestricted research. Most of the research is useless; a tiny fraction is enormously useful. At the moment, lectures subsidize research. By giving lectures, professors are allowed to do research. Fewer professors, less unrestricted research, less innovation. “Wasteful” lecturing might be labor we shouldn’t save.

One thing I like about online classes is the possibility they will connect people who want to learn the same thing, like ordinary classes do. They can help each other, encourage each other, and so on. I have no doubts about the value of this. (I find language partners — I teach them English, they teach me Chinese — way more pleasant and helpful than tutors.)

At Berkeley, I tried to find good lecturers. With two exceptions (Tim White and Steve Glickman) I failed. Almost all lectures, even those by brilliant researchers, were dreary. (A shining exception by Robin Hanson.) They suffered from a lack of stories and a lack of emotion. (At Tsinghua, things are worse. A friend who majors in bioengineering told me that 80% of her teachers lecture by reading from the textbook.) The power of professors over students in some ways resembles the power of doctors over patients. Just as there is little pressure on doctors to understand disease (if antibiotics have bad effects, it doesn’t harm the doctor who prescribed them), there is little pressure on most professors — at least at the elite research universities that produce online lectures — to understand education. At Berkeley, many professors say they teach their undergraduate students “how to think” or “how to think critically”. In fact, they were teaching their students to imitate them. The simplest form of education. This is neither good nor bad — it depends on the student — but it is the opposite of sophisticated.

A few months ago I assigned my Tsinghua students (freshmen) to read 60 pages of The Man Who Would Be Queen by Michael Bailey, a book full of stories and emotion. Any 60 pages, their choice. No test, no written assignment, no grade. One student told me it was the first book in English she’d ever finished. It was so good she couldn’t stop reading. My assignment had changed real-life behavior: what my student read in her spare time. Maybe it changed her tolerance of homosexuality and the tolerance of those around her. My assignment (not a textbook or academic paper, not a fixed reading) and evaluation (none) differed from conventional college teaching. Experiences like this make me wonder what fraction of important learning during college happens due to lecture classes. (In my case, the fraction was zero.) If the fraction is low, it suggests that online learning won’t make much difference.

Assorted Links

Seth Roberts2 Comments

Thanks to Charles Platt and Adam Clemens.

Bariatric Surgery Linked to Acetaminophen Poisoning

Seth Roberts5 Comments

Acetaminophen is a pain killer found in many over-the-counter drugs, such as Tylenol, NyQuil and Sudafed. It can cause liver failure. A new study at the California Pacific Medical Center in San Francisco reports that people who have had bariatric surgery seem to have a much higher risk of this:

Among 54 patients who had suffered acetaminophen-induced liver failure over a three-year period, 17 percent had had weight-loss surgery. . . . Less than 1 percent of the general population has had the surgery.

The study controlled for the possibility that people who have bariatric surgery are more likely to have liver failure unrelated to acetaminophen:

The researchers looked at 101 cases of acute liver failure seen at California Pacific Medical Center, more than half of which were caused by acetaminophen poisoning. Among the nine patients [of the 101] who had had weight-loss surgery, all of them had liver failure caused by acetaminophen overdose.

The article, by a reporter named Erin Allday, goes on to say:

At this time, there is no reason for bariatric surgery patients to be alarmed, and they should continue using acetaminophen if that’s their preferred pain medication or their doctor has prescribed it.

Allday attributes this bizarre advice to unnamed “researchers and weight-loss surgeons.” Of course bariatric surgery patients should be alarmed and cut down or stop using acetaminophen.

The next time someone says “correlation does not equal causation” or belittles epidemiology tell them about this case.

Thanks to David Archer.

Who is the Richest Person in China?

Seth Roberts6 Comments

If you open the American edition of Forbes, you will find articles about the richest people in America. If you open the Russian edition, you will find articles about the richest people in Russia. If you open the Chinese edition, you will find articles about the richest people in America.

A Russian friend of mine noticed this. He happened to know an sophomore economics major at Tsinghua. It is incredibly difficult to get into Tsinghua and the economics major is the most desirable major of all. To be an economics major at Tsinghua you need a test score that is in something like the top 1 out of 100,000. Staggeringly high. My Russian friend asked the Tsinghua economics major, “Who is the richest person in China?”

The economics major didn’t know. He seemed a little angry. “Why should I know? We’ve never been taught that,” he said.

 

Assorted Links

Seth Roberts13 Comments

Thanks to Dave Lull and Alex Chernavsky.

More Sitting, More Diabetes: New Meta-Analysis

Seth Roberts9 Comments

The first evidence linking exercise and health was a study of London bus workers in the 1950s. The drivers, who sat all day, had more heart attacks than the ticket takers on the same buses, who were on their feet all day. It was a huge advance — evidence, as opposed to speculation. The results were taken countless times to imply that exercise reduces heart attacks but epidemiologists understood there were dozens of differences between the two jobs. For example, driving is more stressful than ticket taking. Maybe stress causes heart attacks.

The first time I learned about this study, I focussed on two differences. The ticket takers were more exposed to morning sunlight (on the top deck of double-decker buses) and they were on their feet much more. Maybe both of those things — morning sunlight exposure and standing a lot — improve sleep. Maybe better sleep reduces heart attacks. The London data were not consistent with the claims of aerobic exercise advocates because the ticket takers did nothing resembling aerobic exercise.

Later I discovered that walking an hour/day normalized my fasting blood sugar levels — another effect of “exercise” (but not aerobic exercise). I had data from only one person (myself), but it was experimental data. The treatment difference between the two sets of data being compared (no walking versus walking) was much sharper, in contrast to most epidemiology. I am sure the correlation reflects cause and effect: Walking roughly an hour/day normalized my blood sugar. This wasn’t obvious. The first thing I tried to lower my fasting blood sugar levels was a low-carb diet, which didn’t work. I discovered the effect of long walks by accident.

A recent meta-analysis combined several surveys that measured the correlation of how much you sit with other health measures. The clearest correlation was with diabetes: People who sit more are more likely to get diabetes. Comparing the two extremes (most sitting with most standing), there was a doubling of risk. Because people who stand more walk more, this supports my self-experimental findings.

I found pure standing (no walking), or leisurely (on-off) walking, did not lower fasting blood sugar (which I measured in the morning). After I noticed that walking an hour lowered blood sugar, I tried slacking off: wandering through a store or a mall for an hour. This did not lower fasting blood sugar. I concluded it had to be close-to-nonstop walking. Someday epidemiologists will measure activity more precisely — with Fitbits, for example. I predict the potent part of standing will turn out to be continuous walking. Long before that, you can see for yourself.