http://europepmc.org/abstract/MED/21987445
http://europepmc.org/abstract/MED/17960768
http://europepmc.org/abstract/MED/15450401
http://europepmc.org/abstract/MED/2142531
http://europepmc.org/abstract/MED/12070601
http://europepmc.org/abstract/MED/11406645
http://europepmc.org/abstract/MED/17786186