Name	Info	Provider	Link
	free resource	Scientific Electronic Library Online	https://scielo.isciii.es/scielo.php?script=sci_arttext&pid=S1135-57272010000100007&lng=en&nrm=iso&tlng=en
	free resource	Revista Espanola de Salud Publica	http://www.mscbs.gob.es/biblioPublic/publicaciones/recursos_propios/resp/revista_cdrom/vol84/vol84_1/RS841C_61.pdf