Otto, Karl-Heinz, Leif O. Mönter, Sandra Hof, and Joachim Wirth. “Geographic Experiments in Empirical Research”. Journal of Geography Education 38, no. 3 (September 30, 2010): 133–145. Accessed April 3, 2026. https://www.zgd-journal.de/index.php/zgd/article/view/177.