What does EPA mean by “variability”,”uncertainty”, and “probabilistic modeling”?
Consideration must be given to two important factors throughout the development of a risk assessment: variability and uncertainty. Variability – Refers to the range of toxic response or exposure. For example, the dose that might cause a toxic response can vary from one person to the next depending on factors such as genetic differences, preexisting medical conditions, etc. Exposure may vary from one person to the next depending on factors such as where one works, time spent indoors or out, where one lives, how much people eat or drink, etc. Uncertainty – Refers to our inability to know for sure – it is often due to incomplete data. For example, when assessing the potential for risks to people, toxicology studies generally involve dosing of sexually mature test animals such as rats as a surrogate for humans. Since we don’t really know how differently humans and rats respond, EPA often employs the use of an uncertainty factor to account for possible differences. Additional consideration
