Kaufmann, Katrin. “Non-Formal Education in International Comparison: Patterns of Participation and Investment in Selected European Countries”. International Journal for Research in Vocational Education and Training 2, no. 4 (December 27, 2015): 239-267. Accessed July 20, 2019. https://journals.sub.uni-hamburg.de/hup2/ijrvet/article/view/115.