The Antiplanner’s faithful ally and frequent commenter, C.P. Zilliacus, alerted me to a recent paper published in the Journal of Transport and Health that proves that transit makes people short. Or, at least, it proves this in the same way that other studies have proven that transit makes people healthier or less obese.
The authors of the recent article, University of Minnesota engineers Alireza Ermagun and David Levinson (now at the University of Sydney) review data that “indicate transit use and accessibility by transit are significantly associated with general health.” However, “they are practically insignificant.” In other words, just because something is statistically significant doesn’t mean it is important.
To show this, they compared heights with transit use and show “that transit use and transit accessibility to jobs are negatively correlated with height.” In other words, transit riders are shorter than other people. “We could further engage in data-mining and test other seemingly unrelated phenomenon, and then cherry pick results,” they say. “We prefer not to do that.”
Other researchers haven’t been so reticent. As the Antiplanner has previously noted, people with Smart Growth America once published a peer-reviewed study that found “small but significant associations” between urban sprawl and obesity (as measured by body mass index or BMI). While the peer-reviewed report made no attempt to claim that this proved anything, after it was published the group issued a press release claiming that they had proven that sprawl made people fat.
The Minnesota researchers specifically addressed this type of study, which was based on Centers for Disease Control data. Those data are not broken down by city vs. suburbs, but they are broken down by counties. Ermagun and Levinson call this “big data” because there are hundreds of thousands of observations in the CDC data set, and that many observations means it is possible to find statistical significance in almost anything. But, statistically, “significant” is not the same as “large.”
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For example, using the same data, the Minnesota article finds that “a 1% increase in the share of transit at the county level diminishes the BMI by only 0.0037%.” The result is statistically significant, but that doesn’t mean that riding transit is going to make anyone lose weight.
“There is a thin line between false positive and true negative results,” conclude the researchers. “Transit officials seek to justify the returns of both transit-oriented developments and transit investments and services,” and “the rewards for reporting positive [of transit] effects gives researchers an incentive to select data or analysis method until insignificant results become significant.” Public officials need to take a skeptical view of such claims.
It is a little bit surprising that this article was published by the Journal of Transport and Health as many if not most of the articles in that journal seem to be guilty of finding statistical significance to things that are not practically significant. Transportation does have an affect on health when accidents kill or maim transport users, studies of such accidents make up a minority of the articles in the journal.
In any case, the next time a transit agency claims that transit makes people healthier, we now have a peer-reviewed response. There are a lot better ways for people to lose 0.0037 percent of their weight than to fund a multi-billion-dollar light-rail line.
William M. Briggs, a statistician, has regular diatribes about p value mysticism, and has written a whole book about it, “Uncertainty: The Soul of Modeling, Probability & Statistics.”
People get so caught up in their numbers they forget to look at all of the world, not just their world. And when they do that, the confirmation bias kicks in full force.
Correlation does not equal causality? Fine that throw statistics out the window.
“I don’t believe in Coincidence”
– Batman
There are cheaper ways to lose weight………..like stop freakin eatin so much………..drink more water.
The spike in obesity is not simply overeating… it’s not that we eat, it truly is what we eat.
No one get’s fat eating carrots and lettuce, except a rabbit. The human diet in the last 150 years has transformed, one from conventional foods processed using mere salts and smoking to one of chemical sterility. Human beings digest foods by producing enzymes, these don’t dissolve food, per se. They react to reduce them to chemically simpler substances the body can absorb. However the human body declines in enzyme production even after early age in mid 20’s; and some enzymes our bodies don’t produce at all. Before convenient cooking and food processing, people ate foods…..raw. While food sterilization has resulted in a drastic decline in contaminant related deaths (e-coli, salmonella) it makes food…less efficient to digest.
Raw foods particularly fruits and vegetables are enzymatically alive; the foods have active enzymes within them to help digest more of their food. Cooking high temp destroys enzymes, cooked and processed foods are enzymatically dead which means there are no live enzymes within that food to help with digestion. Once you cook vegetables past 116 degrees Fahrenheit you destroy most of the enzymes. Since foods are supposed to supplement the enzymes our bodies produce in small quantities. Lack of digestive enzymes affects immune system among other things; our bodies go into overtime producing as much as possible to aid in digestion. Foods are broken down but not enzymatically converted into a form soluable to be absorbed. The immune system mistakes these food particles with pathogens and seeks to destroy them; a waste of metabolic energy…in the blood stream they degrade creating toxicity and the nutrients promised are not delivered resulting in deficiency.
Most of what ails us on a daily basis is the result of two things, Toxicity and Deficiency; and the three most important enzymes to handle and replenish.
– lipase, which breaks down fats
– amylase, which breaks down carbohydrates
– proteases and peptidases, which break down proteins.
In the colon, undigested proteins can putrefy, undigested carbohydrates ferment or feed useless bacteria and undigested fats turn rancid. This causes toxicity. These toxins can seep through the intestinal wall and get into the blood stream, which can lead to even more health problems. Plaque buildup in the arteries is partially caused by undigested fats and undigested proteins. 500 LU (moles) of Lipase can break down 4 grams of fat…while that might not sound like much. 12,000 LU (found in one enzyme supplement pill) can break down the fat content in 2 Big Mac’s.
Correllation does not equal causality….unless that train is injecting the fat straight into your ass….