The Adoption of Genetically Engineered Corn and Yield

Many readers of this blog will probably remember the article by Danny Hakim (and the associated infographics) that ran in the New York Times back in October about the "broken promises" of GMOs.  The article prompted some cheers and some legitimate criticisms.  

After that article came out, one thing bugged me a bit.  We have scores of experimental studies showing GMOs (particularly the Bt varieties) increase observed yield, so why don't we see a pronounced effect on aggregate, national yield trends?  At about the same time these thoughts were swirling around in my head, I received a note from Jesse Tack at Kansas State University asking the same.  As it turns out, we weren't the first to wonder about this.  The most recent, 2016, National Academies report on GMOs noted the following:

“the nation-wide data on maize, cotton, or soybean in the United States do not show a significant signature of genetic-engineering technology on the rate of yield increase”

Here is a figure illustrating the phenomenon (from our paper I'll discuss more in a moment).  Despite the massive increase in biotech adoption after 2000, national trend yields don't appear to have much changed.

So we began speculating about possible factors that could be driving this seeming discrepancy between the national, aggregate data on the one hand and the findings from experimental studies on the other, and wondered if aggregation bias might be an issue or whether the lack of controls for changes in weather and climate might be a factor.  One of Jesse's colleagues, Nathan Hendricks, also suggested variation in soil characteristics, which when matched up with different timings of adoption in different areas, might also be an explanation.  

To address these issues, Jesse, Nathan, and I wrote this working paper on the subject, which will be presented in May at conference put on by the National Bureau of Economic Research (NBER).  Here are some of the key findings:

“In this paper, we show that simple analyses of national-level yield trends mask important geographic-, weather-, and soil-related factors that influence the estimated effect of GE crop adoption on yield. Coupling county-level data on corn yields from 1980 to 2015 and state-level adoption of GE traits with data on weather variation and soil characteristics, a number of important findings emerge. First, changes in weather and climatic conditions confound yield effects associated with GE adoption. Without controlling for weather variation, adoption of GE crops appears to have little impact on corn yields; however, once temperature and precipitation controls are added, GE adoption has significant effects on corn yields. Second, the adoption of GE corn has had differential effects on crop yields in different locations even among corn-belt states. However, we find that ad hoc political boundaries (i.e., states) do not provide a credible representation of differential GE effects. Rather, alternative measures based on soil characteristics provide a broad representation of differential effects and are consistent with the data. In particular, we find that the GE effect is much larger for soils with a larger water holding capacity, as well as non-sandy soils. Overall, we find that GE adoption has increased yields by approximately 18 bushels per acre on average, but this effect varies spatially across counties ranging from roughly 5 to 25 bushels per acre. Finally, we do not find evidence that adoption of GE corn led to lower yield variability nor do we find that current GE traits mitigate the effects of heat or water stress.”

To get a sense of the heterogeneity in yield effects, here is a graph of the estimated impacts of adoption of GMOs for counties that differ in terms of their soil's water holding capacity.   

There's a lot more in the paper.

Twitter conversations about GMOs

Last week, an organization called Right Relevance, put out a fascinating post analyzing Twitter interactions surrounding the topic of GMOs during a single month - January 2017.  I don't claim to fully understand all the methods they used or precisely how to interpret the figures they generated, but here's one of their conclusions:

“The retweets-only graph (Fig 2) is even more stark in bringing out the partisanship. It visualizes the echo-chamber like nature of the partisan groups. Also, it shows higher diversity and broader participation on the anti-GMO side.”

The go on to document and rank popular themes, topics, and individuals.  I was a bit curious about the graphs, and even though I didn't recall tweeting much about GMOs in January of 2017, I though I saw my name in tiny font next to NYT Science in the above graph, so I emailed the author of the post asking for a higher resolution figure.  Instead, they sent me the following two graphs focused specifically on my Twitter account (the second one I believe is only based on re-tweets). 

I suppose I shouldn't be at all surprised to recognize most of the names in these figures since they're the same people I'm interacting with on Twitter.  Still, there are many names I don't recognize but who are apparently in my "network".  I'm not sure whether I should be frustrated that my Twitter network on this topic isn't bigger and more diverse or just be thankful for the network I have.  It would also be interesting to see these same figures at different points in time.  From personal experience, I can tell you that when I've had articles on GMOs in the New York Times or Wall Street Journal, I get a lot of people tweeting at me that have widely opposing views.  

Food Demand Survey (FooDS) - February 2017

The February 2017 edition of the Food Demand Survey (FooDS) is now out.  

From the regular tracking portion of the survey, we find that (compared to one month ago) willingness-to-pay (WTP) decreased for all food products, but most especially for chicken wings and the two non-meat products.  For some historical context, I thought I'd also show changes in WTP for steak and ground beef over time and show how they compare with changes in retail prices as reported by the Bureau of Labor Statistics (BLS).  

The above graphs reveals three things.  First, WTP is not the same thing as a price.  WTP is (at least in theory) a "pure" measure of demand, but prices can be affected by demand and by supply-side factors.  Second, despite the above statement, it appears there is some relationship between the two measures as the correlations between WTP and prices are 0.44 for ground beef and 0.55 for steak.  Third, WTP as measured by FooDS is much more volatile from month-to-month than are prices.  

You can read the whole report for the results from the other tracking portions of the survey.

Several new ad hoc questions were added this month to investigate how consumers respond to information about the herbicide glyphosate.  Working with one of my Ph.D. students, Trey Malone, we picked this topic because it is one we thought consumers were unlikely to have much knowledge about but for which there had been many news stories written.  We were interested, in particular, about forms of confirmation bias - where people seek out information that may confirm their prior beliefs, and by the research in cultural cognition, which suggests we choose information to believe based on our "tribe."  

We asked respondent’s willingness-to-pay for organic vs. non-organic apples and granola bars before and after receiving information about glyphosate at GMOs. Respondents were randomly
allocated to one of five treatments. Respondents in the first four treatments were provided an article to read from one of four sources: The Pulse of Natural Health Newsletter, Food Babe, National Review, or Science Magazine. So far this would be a pretty standard study on the effects of information.  Then, in the fifth treatment, respondents were allowed to pick which of the four sources of information they wanted to read (they were given the name of the source and the title of the article).

We will report the full results associated with the effects of information on willingness-to-pay later, however, I will note that the “negative” information about glyphosate from Natural Health and Food Babe had a much bigger effect than the “positive” information from National Review and Science Magazine.

We asked all respondents, “How trustworthy or untrustworthy do you consider each of the following news sources for information regarding food?” They responded on a scale from -5=very untrustworty to +5=very trustworthy. Science Magazine was the most trusted with a mean response of 1.8. Next was National Review at 1.33 followed by Natural Health at 1.28. Far behind (and statistically significantly lower) was the Food Babe at 0.55.

Despite the fact that the Food Babe was the least trusted source of information, in the treatment where individuals could chose which information they wanted to read, 25.4% chose to read the article from the Food Babe. The only source chosen more often was Science Magazine (picked by 40.5% of respondents). Natural Health was picked by 19% and National Review by 15.1%.

How does the media cover GMOs?

I just ran across this interesting article by Katherine Mintz in the Journal of Environmental Studies and Sciences (ungated version here)  Here's a portion of the abstract:

“To understand this divergence in opinion related to GMOs, I analyzed 200 headlines and articles from the Los Angeles Times, New York Times, Wall Street Journal, and Washington Post published between 2011 and 2013. I focused on the key arguments and who is making them. The results showed that newspapers presented 207 favorable and 250 unfavorable mentions of GMOs. The findings revealed the arguments “GMO technical performance” and “potential for environmental harm,” along with actors described as the “biotechnology industry” and “U.S. government,” received more media attention, measured by the frequency of mentions in articles.”

Interestingly, of all  the groups mentioned in media stories, the one that received the least attention was the actual people paying to use the technology: farmers. 

Pew Survey on Consumers, GMOs, and Trust in Science

About a week ago, the PewResearchCenter released a new report (report summary here) on GMOs, organic, and trust in food science.  The report has already been covered quite a bit in the media, but I thought I'd share a few observations on the study's headline results.  

First, the study finds:

“Four-in-ten Americans (40%) say that most (6%) or some (34%) of the foods they eat are organic. ”

It's hard to know what to make of this claim as "some" is a pretty loose category.  One important point to keep in mind here is that USDA data reveal that, except for a few exceptions like lettuce or carrots, for most foods the percent of production that is is organic is typically far less than 5%. 

The study also finds:

“The minority of U.S. adults who care deeply about the issue of GM foods (16%) . . . are also much more likely to consider organic produce healthier”

The finding is consistent with prior research showing that WTP for organic is heavily influenced by the desire to avoid pesticides and GMOs.  In fact, there was a lot of attention given to the organic industry's support of the new mandatory labeling law for GMOs, which allowed disclosure via relatively innocuous QR codes.  The organic industry has worked to make sure people know non-GMO is not synonymous organic.  In other words, these two attributes (organic and non-GMO) are likely demand substitutes for consumers, and the organic industry knows this.  

One of the highlighted conclusions from the study is:

“The divides over food do not fall along familiar political fault lines. ”

I'm not so sure.  While I agree things like concern for GMOs or preferences for organic don't have strong correlations with political ideology, the same can't be said for people's desires to regulate GMOs (say via labels or bans) or subsidize organics .  See, for example, this paper entitled "The political ideology of food" I published in Food Policy in 2012. From the abstract:

“Food ideology was related to conventional measures of political ideology with, for example, more liberal respondents desiring more government involvement in food than more conservative respondents . . .”

As I've written about in the past, I think it is important to separate "food preferences" from "policy preference", and on this last issue, there are big partisan and ideological divides.   

Much of the news coverage I saw about the report focused on the results related to American's trust in scientists and GMOs.  The study reports

“Americans have limited trust in scientists connected with genetically modified foods.”

 The study also reveals only about half the respondents think scientists think GMOs are safe to eat.  Well, Pew's other research shows us that it is more like 88%.  Thus, people under-estimate scientists beliefs about the safety of GMOs.  One might think then, that the answer is to just tell people about the scientific consensus regarding GMOs.  However, my research with Brandon McFadden suggests this probably won't have much affect.  In our study, the biggest determinant of how an individual responded to information about the science on GMOs was their prior belief about the safety of GMOs.  In fact, about a third of the people who thought GMOs were unsafe prior to information said they thought GMOs were even more unsafe after receiving statements from the National Academies of Science, the American Medical Association, etc. indicating GMOs were safe (we called these folk "divergent"); the plurality of people who thought GMOs were unsafe just ignored the scientific information indicating GMOs were safe.  This behavior is a form of motivated reasoning that Dan Kahan has discussed extensively in his work on cultural cognition.  We look for the information that supports our prior beliefs and ignore or discount the rest.  

On this issue of trust in scientists and GMO foods: it is important to note that trust in virtually ALL institutions is down over time.  Gallup has been tracking trust in about a dozen institutions since the 1970s.  Aside from a few exceptions (like the military and police), trust is way down for most institutions.  For example over 65% of people had a great deal or a lot of trust in "church or organized religion" in the 1970s, whereas today the figure is 41%.  For "public schools", confidence was running about 60% in the mid 1970s, but today is only 30%.  Newspapers went from around 40% to now around 20%.  "Big business" from around 30% to now around 18%.   "The medical system" from 80% to 39%.  Similar trends exist for congress, the presidency, organized labor, banks, and so on.   

As a result, it is important to ask how much trust is there in scientists . . . compared to what?  I haven't asked this question specifically in regard to GMOs in particular or food science in general, but a while back I asked on my monthly Food Demand Survey (FooDS):  “How trustworthy is information about meat and livestock from the following sources?” Fifteen sources were listed (the order randomly varied across respondents), and respondents had to place five sources in the most trustworthy category and five sources in the least trustworthy category. A scale of importance was created by calculating the proportion of times a meat and livestock information source as ranked most trustworthy minus the proportion of times it was ranked least trustworthy.

We found:

“The USDA and FDA were reported as most trustworthy with 50% more people indicating the source as most trustworthy than least. A University professor from Harvard were seen as slightly more trustworthy than one from Texas A&M, but both were viewed as less trustworthy than interest groups like the Farm Bureau, the CSPI, or the HSUS.

News organizations, and particularly food companies, were viewed as least trustworthy. Chipotle was the seen as the least trust worthy organization studied – the restaurant chain was placed in the least trustworthy category 69% more often than in the most trustworthy category.”

While individuals scientists at either Harvard or Texas A&M were less trusted than some others perhaps it was because it was phrased a single professor rather than a group of professors.  Indeed, the four top groups are all collections of scientists (among other people).  A subsequent survey asked how much people knew about each of these individuals and institutions, and while CSPI is trusted, it isn't well known.  I suspect people were responding to the word "science".  So, I think there is good reason to suspect people trust scientists as much or more than other societal institutions.

The issue of trust and acceptance of GMOs has been researched quite heavily in the academic literature (e.g., see several studies by Lynn Frewer).  In this paper,  she and coauthors show that people's response to information on GMOs doesn't depend on how much they trust the source per se, but rather it's the other way round: people trust the sources giving them the information that fits with their prior beliefs.  So, again we're back to motivated reasoning.  Still, we should acknowledge some research that shows "information matters."  I've done work on this topic, as has Matt Rousu, Wally Huffman and Jason Shogren.  This last set of researchers show, for example, that relatively uninformed people are influenced by information by interested and third party sources.

There is a lot more in the Pew report, but I think I'll leave it here for now.