Farm questionnaires for monitoring genetically modified crops: a case study using GM maizeKerstin Schmidt, Ralf Wilhelm, Jörg Schmidtke, Lutz Beißner, Wenke Mönkemeyer, Petra Böttinger, Jeremy Sweet and Joachim SchiemannEnviron. Biosafety Res., 7 3 (2008) 163-179DOI: https://doi.org/10.1051/ebr:2008015