BAT has been doing serious research on THR.
http://www.bat.com/group/sites/UK__9D9KCY.nsf/vwPagesWebLive/DO9DCGG2?opendocument&SKN=1
http://www.bat.com/group/sites/UK__9D9KCY.nsf/vwPagesWebLive/DO9DCGG2?opendocument&SKN=1