Kohll i Decker (1998); Ferlini (2000); Geraets-Smits i Peerbooms (2001); Vanbraekel (2001); Inizan (2003); Müller Fauré i Van Riet (2003); Leichtle (2004); Watts (2006); Stamatelaki (2007); Elchinov (2010).