Pagina in costante aggiornamento
http://www.fahealth.org/
http://www.sciencedirect.com/science/article/pii/S1383571802000360
http://www.rrjournal.org/doi/abs/10.1667/0033-7587(2001)156%5B0689%3AHRFREF%5D2.0.CO%3B2