Dose information are limited at best in epidemiology studies. Toxicoligists report the response as an incidence figure, the fraction of animals that exhibit the effect at each dose. Saccharine is the least potent carcinogen detected in animal studies. Continuous toxic responses show increased severity of a condition with increased dose. This is seen in Figure 4 page 165.
Carbon tetrachloride increases the severity of liver damage in rats.
Both continuous and dichotomous responses can occur following exposure to chemicals. If many more animals in animal studies were used then lower risks could be measured. Some chemicals appear to have a threshold levels, others do not. Chemicals that appear to have a threshold level are those with observations that a minimum concentration of a toxic chemical or metabolite must be present before biological changes occur. Also cells can repair certain types of damage.