STUDY: A Meta-Analysis of the Impacts of Genetically Modified Crops

By Community Manager • November 21, 2017

The following is an excerpt from a 2014 paper in PLoS ONE, revealing the results of a metastudy of 147 studies looking at the impact of GMOs. 

Introduction

Despite the rapid adoption of genetically modified (GM) crops by farmers in many countries, public controversies about the risks and benefits continue [1]–[4]. Numerous independent science academies and regulatory bodies have reviewed the evidence about risks, concluding that commercialized GM crops are safe for human consumption and the environment [5]–[7]. There are also plenty of studies showing that GM crops cause benefits in terms of higher yields and cost savings in agricultural production [8]–[12], and welfare gains among adopting farm households [13]–[15]. However, some argue that the evidence about impacts is mixed and that studies showing large benefits may have problems with the data and methods used [16]–[18]. Uncertainty about GM crop impacts is one reason for the widespread public suspicion towards this technology. We have carried out a meta-analysis that may help to consolidate the evidence.

While earlier reviews of GM crop impacts exist [19]–[22], our approach adds to the knowledge in two important ways. First, we include more recent studies into the meta-analysis. In the emerging literature on GM crop impacts, new studies are published continuously, broadening the geographical area covered, the methods used, and the type of outcome variables considered. For instance, in addition to other impacts we analyze effects of GM crop adoption on pesticide quantity, which previous meta-analyses could not because of the limited number of observations for this particular outcome variable. Second, we go beyond average impacts and use meta-regressions to explain impact heterogeneity and test for possible biases.

Our meta-analysis concentrates on the most important GM crops, including herbicide-tolerant (HT) soybean, maize, and cotton, as well as insect-resistant (IR) maize and cotton. For these crops, a sufficiently large number of original impact studies have been published to estimate meaningful average effect sizes. We estimate mean impacts of GM crop adoption on crop yield, pesticide quantity, pesticide cost, total production cost, and farmer profit. Furthermore, we analyze several factors that may influence outcomes, such as geographic location, modified crop trait, and type of data and methods used in the original studies.

Conclusion

This meta-analysis confirms that – in spite of impact heterogeneity – the average agronomic and economic benefits of GM crops are large and significant. Impacts vary especially by modified crop trait and geographic region. Yield gains and pesticide reductions are larger for IR crops than for HT crops. Yield and farmer profit gains are higher in developing countries than in developed countries. Recent impact studies used better data and methods than earlier studies, but these improvements in study design did not reduce the estimates of GM crop advantages. Rather, NGO reports and other publications without scientific peer review seem to bias the impact estimates downward. But even with such biased estimates included, mean effects remain sizeable.

One limitation is that not all of the original studies included in this meta-analysis reported sample sizes and measures of variance. This is not untypical for analyses in the social sciences, especially when studies from the grey literature are also included. Future impact studies with primary data should follow more standardized reporting procedures. Nevertheless, our findings reveal that there is robust evidence of GM crop benefits. Such evidence may help to gradually increase public trust in this promising technology.

To read the entire paper, visit the PLoS ONE website

Posted on December 7, 2017
The term “GMO” typically refers to crops or animals that, through genetic engineering, have had a gene (or a few genes) from a different species inserted into their genome. This is by design to improve a crop or animal with genetic engineering. In fact, me and my colleagues recently published a paper on this very topic that addresses this very topic and gives more details on the plant selection practices used for GE crops.   However, you pick up on something very... Read More
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Posted on December 7, 2017
Nearly all foods today have been genetically modified or altered in some way over thousands of years through selective breeding. However, there are only 10 commercially available GMO crops in the U.S: soybeans, corn (field and sweet), canola, cotton, alfalfa, sugar beets, summer squash, papaya, potatoes and apples.   Below is a table outlining what year the nine crops became commercially available:   Squash 1995 Cotton 1996... Read More
Posted on November 26, 2017
One of the great things about farming is our ability to grow many different crops, while at the same time having the choices to raise them in different fashions, with or without biotech in the crops, especially in crops like corn. This can also be challenging as we have to work with our neighbors to make sure what we are growing doesn't cause a negative effect on what they are growing. This can happen in many different instances.    We raise production seed corn,... Read More
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STUDY: A Meta-Analysis of the Impacts of Genetically Modified Crops
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