For more than ten years now, scientists have been discussing the so-called reproducibility crisis: often, scientific findings cannot be reproduced at a later time and/or in other laboratories, although the studies are carried out under highly standardized conditions. Standardization includes for example the use of genetically identical animals, keeping the animals in identically equipped cages, and carrying out the experiments in exactly the same way. To uncover sources of poor reproducibility, researchers usually try to identify potential confounding factors in the experimental conditions. Confounding factor number one is the experimenter—in other words, the person conducting the experiment. A team headed by behavioral biologists Dr. Vanessa von Kortzfleisch and Prof Helene Richter from the University of Münster (Germany) has now studied precisely this factor in behavioral experiments on mice carried out simultaneously at three different locations. Their study has now been published in the journal PLOS Biology.