Do Your Friends Know You Better Than You Know Yourself?

According to Science News, ​new findings from a longitudinal study following kids since 1976 revealed some surprising results.  Here is the basic study set up according to the authors

Over two years, Montreal students in grades 1, 4 and 7 completed peer evaluations of their classmates and rated them in terms of aggression, likeability and social withdrawal. The students also did self-evaluations

The outcome?​

We found the evaluations from the group of peers were much more closely associated with eventual adult outcomes than were their own personality perceptions from childhood.

​These findings tie nicely in with the research Bailey Norwood and I have conducted over the past several years (see here, here, or here), where we argue (and find) that the best way to predict what someone will do  in the grocery store is often not to ask them what they will do but rather to ask them what they think someone else will do.  

The human mind is skilled in the art of deception (including self deception).  This research reminds me of a quote by Richard Feynman:​

The first principle is that you must not fool yourself—and you are the easiest person to fool.

Economic Impact Review

I can't tell you how many times I've heard reports to the effect: "<<insert paid consul​ting company name here>> has shown that for every $1 the state invests in <<insert your favorite activity here such as a farmers market, beef packing plant, bio-fuel plant, new community center, etc.>> our state/city/town will create <<insert some arbitrarily large number here>> additional jobs.

Some of these claims are no doubt accurate, but all too often it is difficult to know ​how the estimates were generated, what assumptions led to the job-creating estimates, how sensitive the estimates are to the assumptions, or if there are better uses for the investment dollars on the margin.

Fortunately, my occasional co-author Matt Rousu has started up a new website reviewing economic impact studies: Economic Impact Review.​

This is a worthwhile endeavor and I wish him the best of luck with the project.  

Jonathan Haidt on Food

An amusing passage from pg. 13 of Jonathan Haidt's book The Righteous Mind​:

And, why do so many Westerners, even secular ones, continue to see choices about food and sex as being heavily loaded with moral significance? Liberals sometimes say that religious conservatives are sexual prudes for whom anything other than missionary-position intercourse within marriage is a sin.  But conservatives can just as well make fun of liberal struggles to choose a balanced breakfast - balanced among moral concerns about free-range eggs, fair-trade coffee, naturalness, and a variety of toxins, some of which (such as genetically modified corn and soybeans) pose a greater threat spiritually than biologically."

Are GMOs Safe to Eat?

The New York Times ran a story yesterday, highlighting the findings of a paper coming out in the journal Food and Chemical Toxicology.  The study reports that rats fed genetically modified corn developed more tumors and died more quickly than rats not fed genetically modified corn.  

The study will no doubt ignite a firestorm on par with the Monarch butterfly scandal a decade ago (in that episode, Cornell researchers originally reported butterflies being killed by crops containing the Bt gene but later studies published in the Proceedings of the National Academies of Science concluded the effects were negligible).  

In many ways, I applaud the efforts of the French scientists conducting the research.  This is how science is done.  Publish a result.  Be upfront and honest with the methods.  Others will see if they can replicate.  ​

That said, an reasonable person must interpret these new results in light of the existing knowledge on the science of eating GM foods.  The new study did to appear in a vacuum, and there are a large​ number of similar studies finding no such effects from eating GM food.  Given this large baseline of previous research, we can't expect the present study have much influence on our prior beliefs.  This is especially true in light of the fact that the statistical analysis used by at least some of these  authors has been questioned before by none other than the European Food Safety Authority.  And that the supposed causal mechanism between the effects the authors report and the genes involved in conveying resistance to herbicide seems, to me, highly speculative at best. 

I am not on expert on rat feeding trials.  But, the first thing that stood out to me about this study was the very small sample size.  For each gender, there are only 10 rats per treatment group.  It would be difficult, if not impossible, to publish an experimental paper in an ​economics journal with such a small sample size.  Why?  Because with such a small sample you can never really be sure whether the outcomes observed are simply due to chance.  

Using a standard sample size calculation, we can find that with a sample of 10 individuals, the margin of error on a dichotomous variable (like whether a tumor is present or not) is over 30%.  That means, assuming that that the researchers found 50% of rats had a tumor, that if we repeated the study over and over and over, that 95% of the time we'd find expect to find tumor rates between 20% and 70%.  In other words, we cannot have much confidence that the effect the authors observe is "really there" or simply due to chance.  

Obesity Hype

The Robert Wood Johnson Foundation and Trust for America's Health just released a report entitled F as in Fat: How Obesity Threatens America's Future 2012.   The associated press release reports:

For the first time, the annual report includes an analysis that forecasts 2030 adult obesity rates in each state and the likely resulting rise in obesity-related disease rates and health care costs. 

and​

If obesity rates continue on their current trajectories, by 2030, 13 states could have adult obesity rates above 60 percent, 39 states could have rates above 50 percent, and all 50 states could have rates above 44 percent.

​Obesity is out of control!  Or is it?  If we look at the actual data, we can see that no such explosion in obesity rates are occurring.  One group of researchers writing in 2010 in the Journal of the American Medical Association reported that that the prevalence of obesity :    

may have entered another period of relative stability.

Another re-appraisal in 2012 by the same authors using new data in the Journal of the American Medical Association reported

Over the 12-year period from 1999 through 2010, obesity showed no significant increase among women overall

and only slight increases for men​.

Here is the key graph from the JAMA paper​:

As you can see, trends in BMI since 1990-2000 are basically flat.

​So, how is it that the Robert Wood Johnson Foundation and Trust for America's Health can claim run-away trends?  I don't know, but it makes me suspicious of anything else they claim in their report not to mention their policy prescriptions.  

Indeed, it might have done the authors of the report some good  to read  or at least acknowledge what was written in the 2012 JAMA paper (footnotes omitted):

In part because we know relatively little about the precise causes of the trends previously observed, it is hard to predict the future trends in obesity. Several analyses have modeled increasing obesity prevalence as a function of calendar time and then projected future obesity prevalence from these models. These obesity predictions in effect assume that the causal factors for obesity will continue to rise with time or will have an increasing effect over time, and therefore calendar time itself is a reasonable predictor of future obesity prevalence. However, the results reported here and the apparent slowing of trends suggest these may not be valid assumptions and these predictions may be inaccurate.

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