Reader Comments

Post a new comment on this article

Unscientific study design and flawed conclusions

Posted by David_Smith on 03 Sep 2015 at 14:23 GMT

The paper is flawed in its design and presentation of data and does not allow a critical analysis of the data leading to the conclusions:
1. It does not fulfil the requirements of a reliable meta-analysis since the data was pooled from sources with highly contrasting hypotheses not intended to address the same scientific hypothesis.
2. Thus the data used is not scientifically comparable since it was intended for different purposes.
3. The paper grouped herbicides and insecticides together – this in itself is a major flaw.
4. The paper also shows yield increases for herbicide tolerant and insect resistant crops – neither of these traits are yield improvement traits but can be used to prevent yield losses. A scientific approach would have referred to yield loss mitigation rather than yield increase.
5. The paper compares GM performance to non-GM but does not present the non-GM data – this would suggest that the authors are simply relying on the findings of the resources used in the “meta-analysis”.

No competing interests declared.

RE: Unscientific study design and flawed conclusions

mqaim replied to David_Smith on 03 Sep 2015 at 20:12 GMT

I would like to briefly respond to David Smith’s comments, all of which are unconvincing.

1. All of the studies that we included compared the performance of GM and non-GM crops in order to study the technology’s impacts. Hence the data are comparable and can be pooled.

2. See response to point 1.

3. There are indeed differences between the effects of herbicide-tolerant (HT) and insect-resistant (IR) crops. This is why we also differentiate between the two technologies, in addition to the pooled analysis. The results show that HT crops have reduced the costs spent on herbicides but did not significantly affect herbicide quantities. In contrast, IR crops have significantly reduced insecticide quantities and costs.

4. The yields that farmers harvest are higher with these GM traits than without, hence it is a matter of fact that GM crop adoption has increased effective yields. It is true that neither HT nor IR increase the yield potential. This is why we explain in the article “These yield increases are not due to higher genetic yield potential, but to more effective pest control and thus lower crop damage”. David Smith must have overlooked this statement.

5. This comment seems to be based on a misunderstanding of what a meta-analysis actually is. Of course, we use the findings from other studies as they were reported, everything else would not make any sense. The idea of a meta-analysis is to use available results from single studies and analyze what can be learned more broadly from the existing body of literature.

Matin Qaim

No competing interests declared.