Kasselmann, B. von H.; De Beer, J.J. (Johannes Jacobus), 1947-; Vermeulen, Leopold Petrus(Faculty of Economic and Management Sciences, University of Pretoria, 2002-03)
Joubert, Yvonne Trijntje; De Beer, J.J. (Johannes Jacobus), 1947-(Southern African Alliance for Sport Science, Physical Education and Recreation, 2014)
Joubert, Yvonne Trijntje; De Beer, J.J. (Johannes Jacobus), 1947-; De Beer, Hannes, 1947-(Southern African Alliance for Sport Science, Physical Education and Recreation, 2011)