Epidemiology cannot prove causation only association or high probability. Computer modeling is in its infancy with many practical and theoretical challenges to be met. Animal studies are falling out of favor for ethical and scientific reasons. The route of exposure, a variable that can have profound effects on test results, is often impossible to determine. Human populations cannot be controlled which often relies on self reporting of evidence.
Models often have a built in bias from how the software is programmed.
A variable that is related to both the exposure and the outcome. A confounding factor can obscure the relationship between the toxic agent and the adverse health outcome associated with that agent. The way a living organism responds to a toxic substance. The more time spent in contact with a toxic substance, or the higher the dose, the greater the organism's response. A graphic representation of the relationship between the dose administered and the effect produced.