Formal well researched studies from the following folk are worth examining
K.Fagerstrom
D.Hatsukami
P.Newhouse
R.Polosa
K.Farsalinos
Jonathon Foulds
Peter Hajek
Bernd Mayer
Neal Benowitz
JF Etter
Murray Laugesen
Robert West
Ann McNeill
Jamie Brown
Lion Shabab
J Pearson
Andrea Villanti
David Abrams
Ray Niaura
Linda Bauld
C.Delnevo
D. Giavenco
K.Warner
D.Levy
R.Borland
C.Bullen
H.McRobbie
Mike Russell