Autor: Emeterio Díez Puertas
Link: http://www.ehu.eus/zer/hemeroteca/pdfs/zer37-09-diez.pdf
Autor: Joy Elizabeth Hayes & Dana Gravesen
Link: http://www.tandfonline.com/doi/abs/10.1080/19376529.2014.950144?journalCode=hjrs20#