Epidemics begin in one of three model independent ways.
- Exponential (Incidence accelerates rapidly)
- 1918 Influenza (San Francisco, 1918)
- Plague (Bombay, 1905)
- Smallpox (Khuina, Iran, 1977)
- Power (Incidence increases day by day)
- Measles (London, 1948)
- HIV/AIDS (New York City, 1982 – 2002)
- Linear (Incidence remains constant)
- Heart Disease
- Cancer