title: A meta-analysis of the impacts of genetically modified crops.
abstract: BACKGROUND
  Despite the rapid adoption of genetically modified (GM) crops by farmers in many countries, controversies about this technology continue. Uncertainty about GM crop impacts is one reason for widespread public suspicion.
  
  
  OBJECTIVE
  We carry out a meta-analysis of the agronomic and economic impacts of GM crops to consolidate the evidence.
  
  
  METHODS
  Original studies for inclusion were identified through keyword searches in ISI Web of Knowledge, Google Scholar, EconLit, and AgEcon Search.
  
  
  METHODS
  Studies were included when they build on primary data from farm surveys or field trials anywhere in the world, and when they report impacts of GM soybean, maize, or cotton on crop yields, pesticide use, and/or farmer profits. In total, 147 original studies were included.
  
  
  METHODS
  Analysis of mean impacts and meta-regressions to examine factors that influence outcomes.
  
  
  RESULTS
  On average, GM technology adoption has reduced chemical pesticide use by 37%, increased crop yields by 22%, and increased farmer profits by 68%. Yield gains and pesticide reductions are larger for insect-resistant crops than for herbicide-tolerant crops. Yield and profit gains are higher in developing countries than in developed countries.
  
  
  CONCLUSIONS
  Several of the original studies did not report sample sizes and measures of variance.
  
  
  CONCLUSIONS
  The meta-analysis reveals robust evidence of GM crop benefits for farmers in developed and developing countries. Such evidence may help to gradually increase public trust in this technology.
authors.affiliation: Department of Agricultural Economics and Rural Development, Georg-August-University of Goettingen, Goettingen, Germany.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Klümper
authors.affiliation: Department of Agricultural Economics and Rural Development, Georg-August-University of Goettingen, Goettingen, Germany.
authors.forename: Matin
authors.initials: M
authors.lastname: Qaim
mesh_terms: D018556:Crops, Agricultural / Q000191:economics* / Q000254:growth & development*; D030841:Food, Genetically Modified; D006801:Humans; D018803:Models, Economic