Journal impact factor: a brief review
by Eugene Garfield, PhD
CMAJ October 19, 1999 vol. 161 no. 8
Canadian Medical Association Journal
http://www.cmaj.ca/content/161/8/979.full
and
The History and Meaning of the Journal Impact Factor
by Eugene Garfield, PhD
and
Impact factor: a valid measure of journal quality?
Somnath Saha, M.D., M.P.H
J Med Libr Assoc. 2003 January; 91(1): 42–46.