2008 · De Greef, Mathieu H. G., Sprenger, Siska, et al. · University of Groningen research database (University of Groningen / Centre for Information Technology)
2006 · M.H.G. de Greef, S.R. Sprenger, et al. · University of Groningen research database (University of Groningen / Centre for Information Technology)
2005 · Siska R. Sprenger, M.H.G. de Greef, et al. · University of Groningen research database (University of Groningen / Centre for Information Technology)