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HomeConsider ThisLies, Damn Lies, and Statistics: GM Corn, Roundup, and Tumors

Lies, Damn Lies, and Statistics: GM Corn, Roundup, and Tumors

That's Gilles-Eric Séralini on the left. Photo from which is not owned or operated by Séralini or any of his team.
That’s Gilles-Eric Séralini on the left. Photo from which is not owned or operated by Séralini or any of his team.

Here’s a quick recap of Part I of this series:  In November of 2012, the journal “Food and Chemical Toxicology” published a paper by French scientist Gilles-Eric Séralini and his team called “Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize.”  Séralini and his team undertook the study because they were interested in what they saw as indications of toxicity found in the raw data of an earlier 90-day study done by Monsanto.  The results of Séralini’s two year study showed as much as 5 times more liver and kidney disease, and 2 to 3 times more tumors in rats that had eaten Genetically Modified (GM) corn and that had drunk water containing Roundup.  The journal retracted the article in August of 2013, in spite of the objections of its authors, citing problems with the study caused by using too few animals, and because the type of rat used is prone to tumors.  The Editor-in-chief said, “Ultimately the results presented (while not incorrect) are inconclusive, and therefore do not reach the threshold of publication for ‘Food and Chemical Toxicology.'”

Though the Sprague Dawley rat is commonly used for this type of study, and was used for the original Monsanto study, this fact may not overcome concerns about the statistical validity of Séralini’s results.  So let’s take a look at statistics and the suggested guidelines for the number of animals to be used in studies like this.

What Is Statistics?

Statistics is way of testing the likelihood of something happening.  Your insurance company uses statistics to decide how much to charge you for car insurance using information about drivers similar to you and how often they are in accidents.  Weather forecasters use statistical models that compare prior weather conditions with current weather conditions to predict future weather.  If you’re taking any kind of medication, it has been evaluated based on the likelihood that it will help someone like you and the likelihood that you might suffer some kind of side effect.

What all of these uses have in common is that insurance companies don’t have information on all the drivers on the planet, forecasters don’t look at the entire history of weather, and medical researchers don’t study every person taking a drug.  Instead, they use a sample population.  So if you’re running a study, like the one that Séralini’s team did, you need to find similar individuals to represent a larger population and then, you need to figure out how many individuals make up a good sample.  Scientists  have solved the first issue to some degree by using rats with very similar genetic make ups, like the Sprague Dawley rat.  As far as the number of individual rats used in an experiment, it depends on what you’re trying to find out.

Statistics is not an easy discipline.  So, just like every other science, statistics builds on the lessons of researchers who went before.  That means there are protocols that researchers must follow to ensure that they are getting good results.  After all, no one wants to do a 2-year study only to find that they’ve wasted their time.  This also helps those of us non-statisticians to evaluate a study without having to go back to school and get another degree.

Séralini’s Statistics

The Séralini team was primarily interested in potential liver and kidney damage, so they followed the guidance for studies on toxicity presented by the Organization for Economic Cooperation and Development’s (OECD) protocol 453.  For this protocol, the researchers are to use 10 rats per group, at three dose levels for 12 months.  Had they been doing a study on cancer they would have needed 50 rats per group for two years.  The reason for including more animals in the cancer studies is that it gives us a larger sample so that we can tell the difference between animals who were going to get cancer anyway, and animals who were affected by the test substance.  What this means to us is that we can look at the effects on livers and kidneys, but we really can’t say much about whether or not what the rats were eating and drinking caused their tumors.

But the use of statistics goes beyond simply making sure you have enough animals in your sample size.  You have to properly analyze the data that you collect using accepted mathematical models.  The Séralini team used a new type of statistical analysis that left many researchers and professional statisticians scratching their heads.  Since Séralini will not release his raw data, statisticians have taken what they can from the published paper to run their own, more standard analyses and have found a very low likelihood that the rats got tumors as a result of what they were eating.

KathysFullDisclosurePartIIaWhat is the Answer YOU Wanted?

Many of the critiques I’ve read about the Séralini study over the last month or so point out that this is the only study among many that has ever shown negative results for animals fed Genetically Modified grains.  On the other hand, I’ve found articles that describe problems caused by Roundup itself.  Farm families suffered from more miscarriages and premature birth when males were exposed to Roundup.  Subsequent research found that it kills human placental cells at concentrations far below what is used in fields, and that Roundup was at least twice as toxic as glyphosate alone.  Brazilian researchers concluded that Roundup is toxic to rat mothers and causes “developmental retardation of the fetal skeleton” and liver damage to pregnant rats and their fetuses.  But while it may cause those kinds of problems, a study of 57,311 licensed pesticide applicators in Iowa and North Carolina found that glyphosate exposure was not associated with cancer incidence overall.

What I’m most disturbed by is the emotional, and often insulting nature of the comments about and even some of the critiques of the Séralini team’s article.  From my perspective, an opinion about a scientific study has no value if it’s based simply on what the opiner wanted the results to be.  Yes, politics does play a role in science, and yes, it’s possible that the science on both sides of this argument has been tainted from time to time by politics.  That’s part of what it means to be human.  But we have ideals, and we can attempt to live up to them.  We can all play a part in this by paying attention to our own biases, and understanding what science should look like when it has been done well.

As for this study, we really can’t tell what the answer is. More research seems to be in order.

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Kathy Voth
Kathy Voth
I am the founder, editor and publisher of On Pasture, now retired. My career spanned 40 years of finding creative solutions to problems, and sharing ideas with people that encouraged them to work together and try new things. From figuring out how to teach livestock to eat weeds, to teaching range management to high schoolers, outdoor ed graduation camping trips with fifty 6th graders at a time, building firebreaks with a 130-goat herd, developing the signs and interpretation for the Storm King Fourteen Memorial trail, receiving the Conservation Service Award for my work building the 150-mile mountain bike trail from Grand Junction, Colorado to Moab, Utah...well, the list is long so I'll stop with, I've had a great time and I'm very grateful.


  1. HI Kathy,

    I noticed that Seralini did a toxicity study on these rats and reported kidney and liver toxicity.

    However, the information you give to provide an opposite point of view is that roundup and GM may not cause tumours.

    Nobody really has argued with Seralini’s conclusion about the toxic effects of roundup and instead focus on calling the trial a bad cancer study.

    Seralini’s critics are very vocal about GM+Roundup not causing tumours, and, you yourself even cite two studies showing roundup toxicity and then try to balance this with a study showing that it does not increase the incidence of tumours.

    Is this how you are meant to review scientific studies?

    Let me stress this to you again (and anyone who reads this):

    Seralini’s study was NOT a cancer study.
    It was a TOXICITY study.

    (which reported chronic kidney and liver toxicity)

    • Yes, Jonathan, I agree with you. I’m sorry if I wasn’t clear. Let me try again.

      Séralini’s study was on toxicity, and his results show some toxicity to livers and kidneys, as do other studies of Roundup and glyphosate. I included links to a couple of studies showing that. Séralini says he reported the tumor findings because they were surprising and that he agrees that a cancer study should involve more individuals per group. So, it’s up to whoever is next to do the cancer study with more rats per group so that we can know more.

      There are some studies out there showing that incidents of cancer are not associated with GMOs per se, and I also shared a link to one that showed that cancers also did not increase for applicators who worked with Roundup and glyphosate. So, what I’m reading right now is that liver and kidney disease can be linked to Roundup, but maybe not tumors. So more research is required.

      I’m trying my best not to take a side, but to simply explain what I’ve found after a lot of reading. And also, more reading is required. 🙂

  2. Kathy,
    I have to agree with Bill Beaman.

    This article is a plus for On Pasture. When we get into situations like this we are dealing with human nature and all its failings. We all have developed basic beliefs and it is easy to cling to these. You have presented this in a understandable manner that is opening my mind to the, “how”, that we must understand.

    I did not realize that statisticians actually designed the protocol. I had always thought it was something derived by scientists.

    Looking forward to the next segment.

  3. Good follow-up article! The entire Seralini affair sends me one message: why scientific studies designed to evaluate the safety of chemical compounds which will be applied to hundreds of millions of acres and earn their makers billions of dollars are so meager and so subject to accusations of bias. A decision this important should be done on a cohort of animals so large that statistics should be unchallengeable, and the studies should be performed only by third parties chosen by the permitting agency, but with money
    provided by the applicant. If such studies take 2-3 years, so what? What may be inconvenient for the applicant is much less significant than having reliable data on environmental fate, transport and toxicity that can be used to guide product permitting so as to product the public and the environment.

    Of course, with GMOs, the biggest problem is likely to be not human toxicity but rather adverse effects on the property rights, income and market access of non-GMO growers in the vicinity

  4. Kathy,
    I appreciate your explanation of the scientific methods involved and what some of issues were with this particular study by Seralini and his team.

    While the study is inconclusive, it does raise questions and concerns, especially since it is the only long-term study done with GMOs. Just because it’s inconclusive does not mean that it is worth publishing. Many published studies are inconclusive, but are published because they raise questions and concerns needing further study.

    What is discouraging is that the study was retracted from the Journal, despite the fact that the editors could not find anything wrong with the data. The journal specifically noted that there had been no fraud, no misinterpretation of results, and no manipulation of data, which are the normal reasons for retracting a published study.

    Two researchers recently criticized, in Bioethics, the retraction as being politically motivated, and not based on science. The journal recently hired a former Monsanto employee to serve on the editorial team.

    • Hi Paul,

      I did try to look at the politics of this particular situation and decided that there was no way I could figure out who was right and who was wrong. Yes, a former Monsanto employee was hired by the Journal. Richard Goodman worked as a researcher at Monsanto from 1997 to 2004, and since then has been an academic at the University of Nebraska where he does research to evaluate the allergenicity of GM crops and to improve their safety. In his response to allegations that Monsanto pressured the journal to hire him as an Associate Editor to handle the review process of articles related to biotechnology he says that he was unaware of any pressure at all. The journal said they did not have enough reviewers and asked him to fill this role. He reluctantly agreed. So, is he forever tainted by his time at Monsanto? Who am I to say?

      I don’t feel qualified to sit in judgement of Goodman’s qualifications any more than those of Séralini and his team. I think they are likely all very reputable, sincere scientists who are doing their best. That’s why I decided that the only thing to do was look at the science and how it stacks up against accepted protocols. It seems that it meets some and misses others, and yes, it raises questions about the safety of Roundup, as have other studies. The paper meets the requirements of a study of toxicology and some effects were found that are in keeping with other research done on the subject. It doesn’t meet the requirements of a cancer study, and the statistics, when done by other scientists, show that the probability of the tumors being a result of the GM corn is very low.

      That the article was retracted concerns me because it does bring up the specter of politics so strongly, and everywhere I looked the discussion devolves into reputation bashing on both sides. That’s not helpful to trust in science in general. But untangling that ball is beyond me. All I can say at this point is “more research is required.”

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