Gessler, M., and C. . Siemer. “Umbrella Review: Methodological Review of Reviews Published in Peer-Reviewed Journals With a Substantial Focus on Vocational Education and Training Research”. International Journal for Research in Vocational Education and Training, vol. 7, no. 1, Apr. 2020, pp. 91-125, doi:10.13152/IJRVET.7.1.5.