1. The Meaning of It All: Thoughts of a Citizen Scientist;Feynman,1998
2. Institute for Scientific Information (ISI). Available at: http://www.oclc.org/support/services/ezproxy/documentation/db/isi.en.html; Accessed 03.08.13.
3. Science Citation Index. Available at: http://ip-science.thomsonreuters.com/cgi-bin/jrnlst/jloptions.cgi?PC=K; Accessed 30.07.13.
4. Bias in observational studies;Hill,1998
5. Uses of ecologic analysis in epidemiologic research;Mongenstern;Am J Public Health,1982