..But here’s the important part: Simply by chance, if we draw 10 rats from a population in which 72% get tumors after 2 years, we have anywhere from 5 (“t2″) to 10 (“t1″) rats in a treatment group that will develop tumors. Simply due to chance; not due to treatments. If I did not know about this predisposition for developing tumors in Sprague-Dawley rats, and I were comparing these treatment groups, I might be inclined to say that there is indeed a difference between treatment 1 and treatment 2. Only 5 animals developed tumors in treatment 1, and all 10 animals developed tumors treatment 2; that seems pretty convincing. But again, in this case, it was purely due to chance.Read the whole story at @ Control Freaks » Blog Archive » Why I think the Seralini GM feeding trial is bogus:
So my conclusion is that this study is flawed due to the choice of Sprague-Dawley rats, and the duration (2 years) for which the study was conducted. Sprague-Dawley rats appear to have a high probability of health problems after 2 years. And when there is a high probability of health problems, there is a high probability that just by chance you will find differences between treatments, especially if your sample size for each treatment is only 10 individuals.
The Pundit's Comment:
It's what we Pundits call a classic teaching moment
That could be a point. Except that in the work in question, there are 2 control groups (male and female, fed a no GM no Roundup diet), and 18 (yes, eighteen) test groups, fed with different combination of GM and Roundup. Statistics are provided in the original paper for all these groups, are convincing, and easy to verify. Please read it!
ReplyDeleteOh! one last thing (irrelevant in this case, since the statistics are correct, can be verified by all, and have been validated during the peer-reviewed process): You have a 2-shot gun, with only one bullet in it. "Just by chance", you may not kill yourself by putting it on your temple and pressing the trigger. Are you gonna try it? ;-)
That's funny. The paper I read contains NO test for statistical significance of the differences between treatment groups in terms of numbers of deaths.
DeleteThe short version is that your numbers are wrong, David. The study involved 200 mice, assigned into 10 test groups. There were 10 male and 10 female rats in each group. This is very clear in the study.
DeleteThat means your selected excerpt from Andrew Kniss' blog is incorrect. This is not due to chance within the range he outlines - he is either misunderstanding or misrepresenting the study.
Further, your conclusion that choice of tumour-prone rats explains the health problems within two years is also not borne out by the study. The point is that the rats getting the GE corn and/or the weedkiller died or had adverse health effects far sooner than the control group (and the control group lived a typical lifespan for this type of rat).
As to the overall numbers - well there are two points to make.
First of all, It has recently been revealed that the US Department of Agriculture recently backed a feeding study for Genetically Engineered rice, involving 24 subjects receiving the GE rice. In that case there was no control group. Presumably the USDA thinks that 24 is an OK number for a clinical trial. Oh, did I mention that the test subjects in this case were children, in China?
And secondly - I think we can all agree on one thing. If Monsanto thinks that the problem with this Seralini study is that the number of rats was too small, then the logical thing is for them to repeat the study with a much larger number of rats. Then we can all see the outcome. After all, they have never released more than a 90 day study up to now.
What do you think are the chances of that happening?
The numbers in the quick calculation are not mine. I am quoting another blog. I don't represent them as an accurate estimate, but as an understandable illustration of a criticism, a mode of analysis. There is a need to apply a statistical test that the variations in deaths and tumour incidence seen by CRIIGEN are not due to chance. This is a standard matter of interpretation. I'm interested in seeing why there is no test applied in the CRIIGEN paper. Is it because the test fails, or due to incompetence by the authors? You are silent on this issue.
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