Month: April 2009

“Baffling” Link Between Autism and Vinyl Floors

Seth Roberts2 Comments

From Scientific American:

Children who live in homes with vinyl floors, which can emit chemicals called phthalates, are more likely to have autism, according to research by Swedish and U.S. scientists published Monday.

The study of Swedish children is among the first to find an apparent connection between an environmental chemical and autism.

The scientists were surprised by their finding, calling it “far from conclusive.” Because their research was not designed to focus on autism, they recommend further study of larger numbers of children to see whether the link can be confirmed. . . .

The researchers found four environmental factors associated with autism: vinyl flooring, the mother’s smoking, family economic problems and condensation on windows, which indicates poor ventilation.

Here, in a nutshell, are several of the weaknesses with the way epidemiology is currently practiced. I doubt there is anything to this, but who knows? It deserves further investigation. Here’s what could have been better:

1. The researchers did dozens of statistical tests but did not correct for the number of tests. This means there will be a high rate of false positives. The researchers appear to not quite understand this. They don’t need “further study of larger numbers” of subjects — they simply need studies of different populations. The sample size isn’t the problem; the statistical test corrects for that. It is the researchers’ failure to correct for number of tests that makes this evidence so weak.

2. They did their dozens of tests on highly correlated variables. This is like buying two of something you only need one of. A big waste. That they measured something as specific as vinyl flooring implies they gave a long questionnaire to their subjects. Perhaps there were 100 questions. Answers to those questions are likely to be highly correlated. Expensive homes tend to be different in several ways from cheaper homes. The presence/absence of vinyl flooring is likely to be correlated with family economic conditions and condensation on windows (more expensive = better ventilation). The researchers could have used factor analysis or principal components analysis to boil down their long questionnaire into a small number of factors — like 4. So instead of doing 100 tests, they could have done 4 much stronger tests. Then, if there was an unexpected correlation, there would be a good reason to take it seriously.

Someone quoted later in the article gets it completely wrong:

Dr. Philip Landrigan, a pediatrician who is director of the Children’s Environmental Health Center at Mount Sinai School of Medicine, called the results “intriguing, but in my mind preliminary because they are based on very small numbers.”

Nope. Statistical tests correct for sample size. This is like an astronomer saying the sun revolves around the earth. In this article this happens twice.

China and Electric Cars

Seth Roberts5 Comments

According to the New York Times,

Chinese leaders have adopted a plan aimed at turning the country into one of the leading producers of hybrid and all-electric vehicles within three years, and making it the world leader in electric cars and buses after that.

Since I live in Beijing, I am glad to hear this. The story omits an important detail. Every day in Beijing, dozens of electric bikes zoom by me as I ride my non-electric bike. There are 30 or 40 models available, average price about $300. This means when battery makers make car batteries, they will build on a wealth of experience derived from making millions of bike batteries. This isn’t China with cheap labor, as Americans usually imagine the situation; this is China with more experienced labor. It isn’t obvious that American car makers can ever catch up.

The article continues:

Electric vehicles may do little to clear [China’s] smog-darkened sky . . . . China gets three-fourths of its electricity from coal, which produces more soot and more greenhouse gases than other fuels. A report by McKinsey & Company last autumn estimated that replacing a gasoline-powered car with a similar-size electric car in China would reduce greenhouse emissions by only 19 percent. It would reduce urban pollution, however, by shifting the source of smog from car exhaust pipes to power plants, which are often located outside cities.

Please. It is far easier to clean the output of a few hundred power plants than a few hundred million cars.

The United States Department of Energy has its own $25 billion program to develop electric-powered cars and improve battery technology, and will receive another $2 billion for battery development as part of the economic stimulus program enacted by Congress.

I think it’s too late. If the $25 billion were used for rebates to encourage electric car buying, as the Chinese government is doing, that might work, but there aren’t any decent American-made electric cars to be bought.

In related news, Tsinghua University (above all an engineering school) undergraduates who come to America for graduate school now account for more American-trained Ph.D.’s than any American school. In case you think that American engineers are better trained than Chinese ones.