1[3]McCarthy GM, Koval JJ, MacDonald JK, et al. The role of age and population-based differences in the attitudes, knowledge and infection control practices of Canadian dentists. Community Dent Oral Epidemiol, 1999,27(4):298-304.
2[4]Rothman KJ, Greenland S. Modern Epidemiology. 2nd Edition. Philadelphia: Lippincott Williams & Wilkins, 1998. 119.
